Production of silver sulfate grains using carboxylic acid additives

ABSTRACT

An aqueous precipitation process for the preparation of particles comprising primarily silver sulfate, comprising reacting an aqueous soluble silver salt and an aqueous soluble source of inorganic sulfate ion in an agitated precipitation reactor vessel and precipitating particles comprising primarily silver sulfate, wherein the reaction and precipitation are performed in the presence of an aqueous soluble carboxylic acid additive or salt thereof, the amount of additive being a minor molar percentage, relative to the molar amount of silver sulfate precipitated, and effective to result in precipitation of particles comprising primarily silver sulfate having a mean grain-size of less than 70 micrometers.

FIELD OF THE INVENTION

The present invention relates to the production of silver sulfateparticles produced by aqueous precipitation methods, and in particularmicron sized silver sulfate particles produced with uniform sizeemploying carboxylic acid additives or a salt thereof, and the usethereof as an antimicrobial and antiviral agent in polymeric materials.

BACKGROUND OF THE INVENTION

There are various uses for silver sulfate, including as a syntheticreagent; a source of silver in the preparation of catalysts, plasticcomposite materials and various platinum complexes; as well as a sourceof silver in some photographic processes. Recently silver sulfate hasbeen incorporated into plastics and facial creams as an antimicrobialand antifungal agent. To satisfy the demands of many modernapplications, reduction of particle sizes of materials to the micron andnanometer size ranges is often required to take advantage of the highersurface area, surface energy, reactivity, dispersability and uniformityof these size particles; as well as the uniformity and smoothness ofcoatings made thereof, optical clarity due to reduced light scatter,etc., inherent in these forms of matter. In addition, with theminiaturization of the physical size of many objects and devices, asimilar limitation on the physical size of material components is nowcommonly encountered.

Silver sulfate is a commercially available material that is produced byconventional aqueous precipitation methods. The reaction of equimolaramounts of aqueous solutions of silver nitrate and sulfuric acid to fromsilver sulfate was described by Th. W. Richards and G. Jones, Z. anorg.Allg. Chem. 55, 72 (1907). A similar precipitation process using sodiumsulfate as the source of sulfate ion was reported by O. Honigschmid andR. Sachtleben, Z. anorg. Allg. Chem. 195, 207 (1931). An alternatemethod employing the immersion of silver metal in a sulfuric acidsolution was also reported by O. Honigschmid and R. Sachtleben (loc.cit.). Precipitation of finely divided silver sulfate from an aqueoussolution via the addition of alcohol was later reported by H. Hahn andE. Gilbert, Z. anorg. Allg. Chem. 258, 91 (1949). Silver salts arewidely known to be thermally and photolytically unstable, discoloring toform brown, gray or black products. Silver ion may be reduced to itsmetallic state, or oxidized to silver oxide, or react with sulfur toform silver sulfide. Silver sulfate has been observed to decompose bylight to a violet color.

The antimicrobial properties of silver have been known for severalthousand years. The general pharmacological properties of silver aresummarized, e.g., in “Heavy Metals”—by Stewart C. Harvey in ThePharmacological Basis of Therapeutics (Fifth Edition, Chapter 46) byLouis S. Goodman and Alfred Gilman (editors), published by MacMillanPublishing Company, NY, 1975, and “Antiseptics and Disinfectants:Fungicides; Ectoparasiticides”—by Stewart Harvey in The PharmacologicalBasis of Therapeutics (Sixth Edition, Chapter 41) by Louis S. Goodmanand Alfred Gilman (editors), published by MacMillan Publishing Company,NY, 1980. It is now understood that the affinity of silver ion tobiologically important moieties such as sulfhydryl, amino, imidazole,carboxyl and phosphate groups are primarily responsible for itsantimicrobial activity.

The attachment of silver ions to one of these reactive groups on aprotein results in the precipitation and denaturation of the protein.The extent of the reaction is related to the concentration of silverions. The diffusion of silver ion into mammalian tissues isself-regulated by its intrinsic preference for binding to proteinsthrough the various biologically important moieties on the proteins, aswell as precipitation by the chloride ions in the environment. Thus, thevery affinity of silver ion to a large number of biologically importantchemical moieties (an affinity which is responsible for its action as agermicidal/biocidal/viricidal/fungicidal/bacteriocidal agent) is alsoresponsible for limiting its systemic action—silver is not easilyabsorbed by the body. This is a primary reason for the tremendousinterest in the use of silver containing species as an antimicrobial,i.e., an agent capable of destroying or inhibiting the growth ofmicroorganisms, such as bacteria, yeast, fungi and algae, as well asviruses. In addition to the affinity of silver ions to biologicallyrelevant species that leads to the denaturation and precipitation ofproteins, some silver compounds, those having low ionization ordissolution ability, also function effectively as antiseptics. Distilledwater in contact with metallic silver becomes antibacterial even thoughthe dissolved concentration of silver ions is less than 100 ppb. Thereare numerous mechanistic pathways by which this oligodynamic effect ismanifested, i.e., ways in which silver ion interferes with the basicmetabolic activities of bacteria at the cellular level to provide abactericidal and/or bacteriostatic effect.

A detailed review of the oligodynamic effect of silver can be found in“Oligodynamic Metals” by I. B. Romans in Disinfection Sterilization andPreservation, C. A. Lawrence and S. S. Bloek (editors), published by Leaand Fibiger (1968) and “The Oligodynamic Effect of Silver” by A. Goetz,R. L. Tracy and F. S. Harris, Jr. in Silver in Industry, LawrenceAddicks (editor), published by Reinhold Publishing Corporation, 1940.These reviews describe results that demonstrate that silver is effectiveas an antimicrobial agent towards a wide range of bacteria, and thatsilver can impact a cell through multiple biochemical pathways, makingit difficult for a cell to develop resistance to silver. However, it isalso known that the efficacy of silver as an antimicrobial agent dependscritically on the chemical and physical identity of the silver source.The silver source can be silver in the form of metal particles ofvarying sizes, silver as a sparingly soluble material such as silverchloride, silver as a moderately soluble salt such as silver sulfate,silver as a highly soluble salt such as silver nitrate, etc. Theefficiency of the silver also depends on i) the molecular identity ofthe active species—whether it is Ag⁺ ion or a complex species such as(AgSO₄)⁻, etc., and ii) the mechanism by which the active silver speciesinteracts with the organism, which depends on the type of organism.Mechanisms can include, for example, adsorption to the cell wall whichcauses tearing; plasmolysis where the silver species penetrates theplasma membrane and binds to it; adsorption followed by the coagulationof the protoplasm; or precipitation of the protoplasmic albumin of thebacterial cell. The antibacterial efficacy of silver is determined,among other factors, by the nature and concentration of the activespecies, the type of bacteria; the surface area of the bacteria that isavailable for interaction with the active species, the bacterialconcentration, the concentration and/or the surface area of species thatcould consume the active species and lower its activity, and themechanisms of deactivation.

One proposed use of silver based antimicrobials is for textiles. Variousmethods are known in the art to render antimicrobial properties to atarget fiber. The approach of embedding inorganic antimicrobial agents,such as zeolites, into low melting components of a conjugated fiber isdescribed in U.S. Pat. No. 4,525,410 and U.S. Pat. No. 5,064,599. Inanother approach, the antimicrobial agent can be delivered during theprocess of making a synthetic fiber such as those described in U.S. Pat.No. 5,180,402, U.S. Pat. No. 5,880,044, and U.S. Pat. No. 5,888,526, orvia a melt extrusion process as described in U.S. Pat. No. 6,479,144 andU.S. Pat. No. 6,585,843. In still yet another process, an antimicrobialmetal ion can be ion exchanged with an ion exchange fiber as describedin U.S. Pat. No. 5,496,860.

High-pressure laminates containing antimicrobial inorganic metalcompounds are disclosed in U.S. Pat. No. 6,248,342. Deposition ofantimicrobial metals or metal-containing compounds onto a resin film ortarget fiber has also been described in U.S. Pat. No. 6,274,519 and U.S.Pat. No. 6,436,420.

In particular, the prior art has disclosed formulations that are usefulfor highly soluble silver salts having aqueous solubility products,herein referred to as pKsp, of less than 1. In general, these silversalts require the use of hydrophobic addenda to provide the desiredcombination of antimicrobial behavior and durability. Conversely, it isalso known that very insoluble metallic silver particles, having a pKspgreater than 15, would require hydrophilic addenda to provide thedesired combination of antimicrobial behavior and durability. Thereexists a need to provide sparingly soluble silver salts in the range ofpKsp from about 3-8, which can be highly efficient in antimicrobial andantiviral behavior when incorporated directly into plastics andpolymeric materials.

The use of an organo-sulfate or organo-sulfonate additive as a means ofcontrolling the particle size of precipitated silver sulfate isdescribed in U.S. Pat. No. 7,261,867. Use of an inorganic additivecompound that contains a cation capable of forming a sulfate salt thatis less soluble than silver sulfate or a halide anion or an oxyanioncapable of forming a silver salt that is less soluble than silversulfate, as a means of controlling the particle size of precipitatedsilver sulfate is disclosed in U.S. patent application Ser. No.11/694,582 filed Mar. 30, 2007. However, the inclusion of substantialamounts of organic character in additives to silver sulfate materialshas been shown to compromise the thermal stability. Polymer compositescomprising a thermoplastic polymer compounded with a phenolicantioxidant, an organo-disulfide antioxidant, and a silver-basedantimicrobial agent, the specified combination of antioxidantstabilizers being superior in inhibiting undesirable discoloration, isdisclosed in U.S. patent application Ser. No. 11/669,830 filed Jan. 31,2007. Alternatively, the use of bromate or iodate ion to inhibit thethermal or light induced discoloration of melt-processed polymerscompounded with silver-based antimicrobial agents is disclosed in U.S.patent application Ser. No. 11/694,390 filed Mar. 30, 2007.

Parasiticidal preparations of metal alkylsulphates and metal detergentsulphonates are described by Duperray in GB 1,082,653. Disclosuresinclude the preparation of silver salts of alkylsulphates (specifically,silver laurylsulfphate and silver lauroylamino-ethylsulphate) and thesilver salt of an alkylarylsulphonate (specifically, silverdodecylbenzenesulphonate). These compounds are prepared by reacting anexcess of the alkylsulphate or alkylarylsulphonate with silverhydroxide, to form a neutral salt (or 1:1 adduct). While considerableefficacy in destroying parasitic protozoa such as coccidiae andhistomones resulted when these compounds were added to the drinkingwater of diseased chickens, turkeys and cattle, neutral silver salts ofthese kinds contain too much organic character for use in someapplications. Specifically, silver laurylsulphate has been observed tobe extremely discolored when added into even a relatively lowtemperature (about 170° C.) melt of a polyolefin. This result is typicalof polymer melt additives that either contain too much unstable organiccharacter or are simply added in an excessive amount.

An antimicrobial masterbatch formulation is disclosed in JP 2841115B2wherein a silver salt and an organic antifungal agent are combined in alow melting wax to form a masterbatch with improved dispersibility andhandling safety. More specifically, silver sulfate was sieved through a100 mesh screen (particles sizes less than about 149 microns), combinedwith 2-(4-thiazolyl)benzimidazole and kneaded into polyethylene wax.This masterbatch material was then compounded into polypropylene, whichwas subsequently injection molded into thin test blocks. These testblocks were reported to be acceptable for coloration and thermalstability, while exhibiting antibacterial properties with respect to E.coli and Staphylococcus, and antifungal properties with respect toAspergillus niger. Similar masterbatches are also described in JP03271208, wherein a resin discoloration-preventing agent (e.g. UV lightabsorbent, UV light stabilizer, antioxidant) is also incorporated.

An antimicrobial mixture of zinc oxide and silver sulfate on aninorganic powder support is disclosed in JP 08133918, wherein theinorganic powder support is selected from calcium phosphate, silica gel,barium sulfate and titanium oxide. The average primary particle diameterof the inorganic carrier powder is preferably ≦10 microns, morepreferably ≦5 microns. The amount of silver sulfate supported is ≧0.04%and <5.0%, especially preferably ≧0.3% and <1.8%. The ratio of zincoxide to the inorganic powder supporting silver sulfate is selected fromthe range of 0.2:99.8 to 30:70. The low overall content ofantimicrobially active silver sulfate (<5.0%) in these particulatemixtures requires a relatively high loading of the mixture into apolymer or other substrate.

Silver sulfate has been proposed as an antimicrobial agent in a numberof medical applications. Incorporation of inorganic silver compounds inbone cement to reduce the risk of post-operative infection following theinsertion of endoprosthetic orthopaedic implants was proposed andstudied by J. A. Spadaro et al (Clinical Orthopaedics and RelatedResearch, 143, 266-270, 1979). Silver chloride, silver oxide, silversulphate and silver phosphate were incorporated inpolymethylmethacrylate bone cement at 0.5% concentration and shown tosignificantly inhibit the bacterial growth of Staphylococcus aureus,Escherichia coli and Pseudomonas aeruginosa. Antimicrobial wounddressings are disclosed in U.S. Pat. No. 4,728,323; wherein a substrateis vapor or sputter coated with an antimicrobially effective film of asilver salt, preferably silver chloride or silver sulfate. Antimicrobialwound dressings are disclosed in WO2006113052A2; wherein aqueous silversulfate solutions are dried onto a substrate under controlled conditionsto an initial color, which is color stable for preferably one week underambient light and humidity conditions. An antimicrobial fitting for acatheter is disclosed in U.S. Pat. No. 5,049,140; wherein a proposal tofabricate a tubular member composed of a silicone/polyurethane elastomerin which is uniformly dispersed about 1 to 15% wt. of an antimicrobialagent, preferably silver sulfate, is described. A moldable plasticcomposite comprising cellulose and a urea/formaldehyde resin isdisclosed in WO2005080488A1, wherein a silver salt, specifically silversulfate, is incorporated to provide a surface having antiviral activityagainst SARS (severe acute respiratory syndrome) corona virus.

Despite various references to the proposed use of silver salts asantimicrobial agents in various fields as referenced above, there arelimited descriptions with respect to approaches in the prior art forpreparing silver salts, specifically silver sulfate, of sufficientlysmall grain-size and of optimal grain-size distribution as may bedesired for particular applications. A need exists, in particular, toprovide antimicrobial agents such as silver salts, more specificallysilver sulfate, in controlled particular sizes for use in plastics andpolymer containing materials with improved antimicrobial efficacy,reduced cost and enablement of more robust manufacturing processes.

SUMMARY OF THE INVENTION

In accordance with one embodiment, the present invention is directedtowards a process comprising reacting an aqueous soluble silver salt andan aqueous soluble source of inorganic sulfate ion in an agitatedprecipitation reactor vessel and precipitating particles comprisingprimarily silver sulfate, wherein the reaction and precipitation areperformed in the presence of an aqueous soluble carboxylic acid additiveor salt thereof, the amount of additive being a minor molar percentage,relative to the molar amount of silver sulfate precipitated, andeffective to result in precipitation of particles comprising primarilysilver sulfate having a mean grain-size of less than 70 micrometers.

The present invention provides a facile and rapid method of productionof substantially free flowing powders of micrometer grain-size primarilysilver sulfate particles with uniform morphology and size produced byaqueous precipitation methods well adapted to large-scale commercialproduction. The precipitated micron-sized particle grains are stabilizedagainst excessive aggregation by the carboxylic acid additive or saltthereof, resulting in less agglomerated aqueous dispersions and morereadily dispersed dry or substantially dry powders of silver sulfate.The invention avoids or limits need for any additional and potentiallycomplicating steps of milling, grinding and sieving that may be requiredto obtain equivalent-sized particle grains of silver sulfate frommaterials precipitated in the absence of the carboxylic acid additive orsalt thereof employed in the invention.

The materials provided by the invention impart improved antibacterial,antifungal and antiviral properties to mixtures and composites of thematerials of the invention in combination with plastics, polymers,resins, etc.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the process of the present invention, an aqueoussolution of a soluble silver salt and an aqueous solution of a source ofinorganic sulfate ion may be added together under turbulent mixingconditions in a precipitation reactor. In the absence of the invention,such a precipitation reaction has been found to typically result insubstantial agglomeration (aggregation) of the precipitated primarycrystallites such that the actual precipitated particle grain-sizes maybe significantly larger than may be desired for some applications. Inaccordance with the present invention, it has been found that performingthe precipitation of silver sulfate particles in the reactor in thepresence of an effective minor amount of specified carboxylic acidadditive or salt thereof enables obtaining stable, micrometer size (e.g.less than about 70 micrometer) dispersed primarily silver sulfateparticles, of a grain-size smaller than that obtained in the absence ofthe carboxylic acid additive or salt thereof.

The specified carboxylic acid additives or salts thereof employed in thepresent invention refer to monocarboxylic or multicarboxylic acids, thelatter including, for instance, dicarboxylic, tricarboxylic andtetracarboxylic acids. The carboxylic acid additive or salt thereof maybe monomeric or polymeric, the latter containing substituent groupscomprising one or more carboxylic acid groups or the salt thereof Thesalt form of the carboxylic acid additive employed in the invention maybe formed by exchanging, in whole or in part, the acidic protons of thecarboxylic acid groups with other cations, including, for example,alkali metal cations (such as sodium, potassium, rubidium and cesium),alkaline earth metal cations (such as calcium, magnesium, strontium andbarium) and ammonium ion. The carboxylic acid additive or salt thereofpreferably has an aqueous solubility of at least 1 g/L.

The carboxylic acid additive or salt thereof is added to theprecipitation reactor as a minor component (i.e., less than 50 molarpercent), relative to the molar amount of silver, effective forobtaining stable, primarily silver sulfate particles of a mean size lessthan 70 microns. As demonstrated in the examples, effective amounts ofadditive required may depend upon the specific carboxylic acid additiveor salt thereof employed, but generally will typically be an amountproviding greater than 0.7 molar percent of carboxylic acid orcarboxylate groups, based on the molar amount of silver reacted,although lower concentrations may also be effective depending uponoptimized precipitation reaction conditions. Determination of theminimum or optimum effective amount of an additive employed in theinvention is well within the ability of someone of ordinary skill in theart. By restricting the amount of additive to a minor molar amountrelative to the amount of silver, negative attributes associated withthe organic character of the additive may be controlled in the resultingprecipitated particles comprising primarily silver sulfate, while theminor amounts of additive may still be effective to achieve the desiredprecipitated particle size. In preferred embodiments of the invention,additives are selected which are effective at molar amounts less than 10percent, more preferably less than 5 percent, and most preferably lessthan 1 percent, based on the molar amount of silver. In variousembodiments of the invention, the carboxylic acid additive or saltthereof may be added to the reactor before, during and/or after additionof the aqueous soluble silver salt solution to the reactor.

Soluble silver salts that may be employed in the process of theinvention include silver nitrate, acetate, propionate, chlorate,perchlorate, fluoride, lactate, etc. Inorganic sulfate ion sourcesinclude sulfuric acid, ammonium sulfate, alkali metal (lithium, sodium,potassium, rubidium, cesium) sulfate, and alkaline earth metal (such asmagnesium) sulfate, transition metal (such as zinc, cadmium, zirconium,yttrium, copper, nickel, iron) sulfate, etc. In a preferred embodimentof the invention, the soluble silver salt employed is silver nitrate andthe source of inorganic sulfate ion is ammonium sulfate or sulfuricacid, more preferably ammonium sulfate.

Turbulent mixing conditions employed in precipitation reactors inaccordance with the process of the invention may be obtained by means ofconventional stirrers and impellers. In a specific embodiment of theinvention, the reactants are preferably contacted in a highly agitatedzone of a precipitation reactor. Preferred mixing apparatus, which maybe used in accordance with such embodiment, includes rotary agitators ofthe type which have been previously disclosed for use in thephotographic silver halide emulsion art for precipitating silver halideparticles by reaction of simultaneously introduced silver and halidesalt solution feed streams. Such rotary agitators may include, e.g.,turbines, marine propellers, discs, and other mixing impellers known inthe art (see, e.g., U.S. Pat. No. 3,415,650; U.S. Pat. No. 6,513,965,U.S. Pat. No. 6,422,736; U.S. Pat. No. 5,690,428, U.S. Pat. No.5,334,359, U.S. Pat. No. 4,289,733; U.S. Pat. No. 5,096,690; U.S. Pat.No. 4,666,669, EP 1156875, WO-0160511).

While the specific configurations of the rotary agitators which may beemployed in preferred embodiments of the invention may varysignificantly, they preferably will each employ at least one impellerhaving a surface and a diameter, which impeller is effective in creatinga highly agitated zone in the vicinity of the agitator. The term “highlyagitated zone” describes a zone in the close proximity of the agitatorwithin which a significant fraction of the power provided for mixing isdissipated by the material flow. Typically, it is contained within adistance of one impeller diameter from a rotary impeller surface.Introduction of a reactant feed stream into a precipitation reactor inclose proximity to a rotary mixer, such that the feed stream isintroduced into a relatively highly agitated zone created by the actionof the rotary agitator provides for accomplishing meso-, micro-, andmacro-mixing of the feed stream components to practically usefuldegrees. Depending on the processing fluid properties and the dynamictime scales of transfer or transformation processes associated with theparticular materials employed, the rotary agitator preferably employedmay be selected to optimize meso-, micro-, and macro-mixing to varyingpractically useful degrees.

Mixing apparatus that may be employed in one particular embodiment ofthe invention includes mixing devices of the type disclosed in ResearchDisclosure, Vol. 382, February 1996, Item 38213. In such apparatus,means are provided for introducing feed streams from a remote source byconduits that terminate close to an adjacent inlet zone of the mixingdevice (less than one impeller diameter from the surface of the mixerimpeller). To facilitate mixing of multiple feed streams, they may beintroduced in opposing direction in the vicinity of the inlet zone ofthe mixing device. The mixing device is vertically disposed in areaction vessel, and attached to the end of a shaft driven at high speedby a suitable means, such as a motor. The lower end of the rotatingmixing device is spaced up from the bottom of the reaction vessel, butbeneath the surface of the fluid contained within the vessel. Baffles,sufficient in number to inhibit horizontal rotation of the contents ofthe vessel, may be located around the mixing device. Such mixing devicesare also schematically depicted in U.S. Pat. Nos. 5,549,879 and6,048,683; the disclosures of which are incorporated by reference.

Mixing apparatus that may be employed in another embodiment of theinvention includes mixers that facilitate separate control of feedstream dispersion (micromixing and mesomixing) and bulk circulation inthe precipitation reactor (macromixing), such as described in U.S. Pat.No. 6,422,736, the disclosure of which is incorporated by reference.Such apparatus comprises a vertically oriented draft tube, a bottomimpeller positioned in the draft tube, and a top impeller positioned inthe draft tube above the first impeller and spaced there from a distancesufficient for independent operation. The bottom impeller is preferablya flat blade turbine (FBT) and is used to efficiently disperse the feedstreams, which are added at the bottom of the draft tube. The topimpeller is preferably a pitched blade turbine (PBT) and is used tocirculate the bulk fluid through the draft tube in an upward directionproviding a narrow circulation time distribution through the reactionzone. Appropriate baffling may be used. The two impellers are placed ata distance such that independent operation is obtained. This independentoperation and the simplicity of its geometry are features that make thismixer well suited in the scale-up of precipitation processes. Suchapparatus provides intense micromixing, that is, it provides very highpower dissipation in the region of feed stream introduction.

Once formed in an aqueous precipitation process in accordance with theinvention, the resulting ultra-fine silver sulfate particles may bewashed, dried and collected as a white free-flowing powder. In terms ofparticle size metrics, the precipitation process preferably results inproducing both a small primary crystallite size and a small grain-size,along with a narrow grain-size distribution.

In discussing silver sulfate particle morphology and metrology it isimportant to clearly understand the definitions of some elementary andwidely used terms. By primary crystallite size, one refers to that sizewhich is commonly determined by X-Ray Powder Diffraction (XRPD). A widerXRPD line width implies a smaller primary crystallite size.Quantitatively, the crystallite size (t) is calculated from the measuredX-ray peak half width (B (radians)), the wavelength of the X-ray (λ),and the diffraction angle (θ) using the Scherrer equation:

t=0.9λ/(B cos θ)

See B. D. Cullity, “Elements of X-Ray Diffraction” (1956) Addison-WesleyPublishing Company, Inc., Chapter 9.

From a structure view, a crystallite is typically composed of many unitcells, one unit cell being the most irreducible representation of thecrystal structure. The primary crystallite size should not be confusedwith the final grain-size. The final grain-size is determined by howmany of the crystallites agglomerate. Typically, the grain-sizemeasurement, including size frequency distribution, can be determinedfrom light scattering measurements provided, for instance, by an LA-920analyzer available from HORIBA Instruments, Inc. (Irvine, Calif., USA).It is important to make the distinction that having a small primarycrystallite size does not guarantee a small final grain-size—this mustbe measured separately from the XRPD spectrum. However, a large primarycrystallite size will preclude a small final grain-size. Thus to fullycharacterize a particulate dispersion one would need a knowledge offinal grain-size (e.g. HORIBA), size-frequency distribution embodied,for example, in the standard deviation (e.g. HORIBA), and primarycrystallite size (XRPD).

In preferred embodiments, silver sulfate particles obtained inaccordance with the invention can be combined with a melt-processedpolymer (e.g. thermoplastic and thermoset) to form a composite, wherethe composite is defined as the silver sulfate dispersed in the polymerafter thermal processing. The preferred thermoplastic polymers suitablefor making composites are those polymeric compounds having good thermalstability and a range of melt index, preferably from about 0.3 to about99. The weight ratio of silver sulfate to thermoplastic polymer in thecomposite may vary widely depending on application. However, it ispreferred that the ratio is ≧0.01:99.99, more preferably ≧ about 1:99,and most preferably ≧ about 5:95, particularly if the desired result ishigh antimicrobial efficacy.

A preferred method for making the composite of the silver sulfate,together with any optional addenda, in polymer is melt blending with thethermoplastic polymer using any suitable mixing device such as a singlescrew compounder, blender, paddle compounder such as a Brabender,spatula, press, extruder, or molder such as an injection molder.However, it is preferred to use a suitable batch mixer, continuous mixertwin-screw compounder such as a PolyLab or Leistritz, to ensure propermixing and more uniform dispersal. Twin-screw extruders are built on abuilding block principle. Thus, mixing of silver sulfate, temperature,mixing rotations per minute (rpm), residence time of resin, as well aspoint of addition of silver sulfate can be easily changed by changingscrew design, barrel design and processing parameters. Similar machinesare also provided by other twin- screw compounder manufacturers likeWerner and Pfleiderrer, Berstorff, and the like, which can be operatedeither in the co-rotating or the counter-rotating mode.

One method for making the composite is to melt polymer in a glass, metalor other suitable vessel, followed by addition of the silver sulfatesalt of this invention. The polymer and silver sulfate are mixed using aspatula until the silver sulfate is uniformly dispersed in the polymer.Another method for making the composite is to melt the polymer in asmall compounder, such as a Brabender compounder, followed by additionof the silver sulfate salt of this invention. The polymer and silversulfate are mixed using the compounder until the silver sulfate isuniformly dispersed in the polymer. Alternatively, the silver sulfate ofthis invention can be predispersed in the polymer followed by additionof this mixture to the mixing device. Yet, in another method such as inthe case of a twin-screw compounder, this compounder is provided withmain feeders through which resins are fed, while silver sulfate might befed using one of the main feeders or using the side stuffers. If theside stuffers are used to feed the silver sulfate then screw designneeds to be appropriately configured. The preferred mode of addition ofsilver sulfate material to the thermoplastic polymer is through the useof the side stuffer, though top feeder can be used, to ensure properviscous mixing and to ensure dispersion of the silver sulfate throughthe polymer matrix as well as to control the thermal history. In thismode, the thermoplastic polymer is fed using the main resin feeder, andis followed by the addition of the silver sulfate through the downstreamside stuffer. Alternatively, the polymer and silver sulfate can be fedusing the main feeders at the same location. In yet another embodimentthe silver sulfate can be pre-dispersed in a thermoplastic polymer in amasterbatch, and further diluted in the compounder. As before, themasterbatch and the thermoplastic polymer can be fed through the mainresin feeder and/or the side or top feeder, depending on specificobjectives. It is preferred that the resultant composite materialobtained after compounding is further processed into pellets, granules,strands, ribbons, fibers, powder, films, plaques and the like, orinjection molded into parts, for subsequent use.

Polymers suitable to the invention include those melt-processed betweenabout 60-500° C. A non-limiting list of such polymeric materialsinclude:

1. Polymers of monoolefins and diolefins, for example polypropylene,polyisobutylene, polybut-1-ene, poly-4-methylpent-1-ene,polyvinylcyclohexane, polyisoprene or polybutadiene, as well as polymersof cycloolefins, for instance of cyclopentene or norbornene,polyethylene (which optionally can be crosslinked, known as PEX), forexample high density polyethylene (HDPE), high density and highmolecular weight polyethylene (HDPE-HMW), high density and ultrahighmolecular weight polyethylene (HDPE-UHMW), medium density polyethylene(MDPE), low density polyethylene (LDPE), linear low density polyethylene(LLDPE), (VLDPE) and (ULDPE).

2. Mixtures of the polymers mentioned above, for example mixtures ofpolypropylene with polyisobutylene, polypropylene with polyethylene (forexample PP/HDPE, PP/LDPE) and mixtures of different types ofpolyethylene (for example LDPE/HDPE).

3. Copolymers of monoolefins and diolefins with each other or with othervinyl monomers, for example ethylene/propylene copolymers, linear lowdensity polyethylene (LLDPE) and mixtures thereof with low densitypolyethylene (LDPE), propylene/but-1-ene copolymers,propylene/isobutylene copolymers, ethylene/but-1-ene copolymers,ethylene/hexene copolymers, ethylene/methylpentene copolymers,ethylene/heptene copolymers, ethylene/octene copolymers,ethylene/vinylcyclohexane copolymers, ethylene/cycloolefin copolymers(e.g. ethylene/norbornene like COC), ethylene/1-olefins copolymers,where the 1-olefin is generated in-situ; propylene/butadiene copolymers,isobutylene/isoprene copolymers, ethylene/vinylcyclohexene copolymers,ethylene/alkyl acrylate copolymers, ethylene/alkyl methacrylatecopolymers, ethylene/vinyl acetate copolymers or ethylene/acrylic acidcopolymers and their salts (ionomers) as well as terpolymers of ethylenewith propylene and a diene such as hexadiene, dicyclopentadiene orethylidene-norbornene; and mixtures of such copolymers with one anotherand with polymers mentioned in 1) above, for examplepolypropylene/ethylene-propylene copolymers, LDPE/ethylene-vinyl acetatecopolymers (EVA), LDPE/ethylene-acrylic acid copolymers (EAA),LLDPE/EVA, LLDPE/EAA and alternating or random polyalkylene/carbonmonoxide copolymers and mixtures thereof with other polymers, forexample polyamides.

4. Vinyl polymers and copolymers used in thermoplastics, such aspoly(vinyl chloride) and derivatives thereof; polystyrene andderivatives thereof; poly(acrylic acid); polyacrylates;polycyanoacrylate; poly(alkyl acrylates) such as poly(methyl acrylate)and poly(ethyl acrylate); poly(methacrylic acid) (PMAA); poly(methylmethacrylate) (PMMA); polyacrylamide; polyacrylonitrile;polyisobutylene; polybutenes; polydicyclopentadiene;polytetrafluoroethylene (TEFLON); polytrichlorofluoroethylene;polychlorotrifluoroethylene; poly(vinyl acetate); poly(vinyl alcohol);poly(vinyl butyral) (BUTVAR™); poly(N-vinyl carbazole), poly(vinylchloride-acetate); poly(vinyl ethers); poly(vinylidene chloride);poly(vinylidene fluoride); poly(vinyl fluoride); poly(vinyl pyrolidone);poly(vinyl pyrolidinone); allyl resins (crosslinked diallyl and triallylesters).

5. Polyesters such as the commercially available linear polyesters, forexample poly(ethylene terephthalate) (PET), poly(trimethyleneterephthalate) (PIT), poly(butylene terephthalate) (PBT), poly(ethylenenaphthalene-2,6-dicarboxylate) (PEN), poly(4-hydroxybenzoate),poly(bisphenol A terephthalate/isophthalate),poly(1,4-dihydroxymethylcyclohexyl terephthalate), polycarbonate (suchas bisphenol A polycarbonate), polycaprolactone, poly(glycolic acid),poly(lactic acid); the bacterial polyesters known collectively aspoly(hydroxy alkanoates) (PHA), such as poly(3-hydroxybutyrate) (PHB),phenyl-substituted PHA and unsaturated PHA; and the man-made randomcopolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV); thehyperbranched polyesters; the crosslinked or network polyesters commonlycalled alkyds or polyester resins, including i) the saturated polyesterresins that utilize polyfunctional alcohols and acids, such as glycerol,pentaerythritol, sorbitol, citric acid, trimellitic acid, orpyromellitic dianhydride, to crosslink during the esterificationreaction, typically used to prepare oil-modified alkylds and styrenatedalkyds, and ii) the unsaturated polyester resins that utilize doublebonds incorporated into the polyester backbone to crosslink in aseparate addition polymerization reaction step.

6. Polyamides and polypeptides, including, for example, the commerciallyavailable commodity nylons such as Nylon 6 (polycaprolactam) and Nylon66 [poly(hexamethylene adipamide)]; commercial specialty nylons such asNylon 7 [poly(7-heptanamide)], Nylon 8 [polycapryllactam], Nylon 9[poly(9-nonanamide)], Nylon 11 [poly(11-undecanamide)], Nylon 12[polylauryllactam], Nylon 46 [poly(tetramethylene adipamide)] Nylon 69[poly(hexamethylene azelamide)] Nylon 610 [poly(hexamethylenesebacamide)] Nylon 612 [poly(hexamethylene dodecanediamide)];commercially available polymers poly(methylene-4,4′-dicyclohexylenedodecanediamide), poly(1,4-cyclohexylenedimethylene suberamide),poly(m-phenylene isophthalamide) (DuPont NOMEX™), poly(p-phenyleneterephthalamide) (DuPont KEVLAR™), poly(2,4,4-trimethylhexamethyleneterephthalamide), poly(2,2,4-trimethylhexamethylene terephthalamide);other nylons such as Nylon 1 and derivatives thereof, Nylon 3(poly-β-alanine), Nylon 4, Nylon 5; branched nylons; wholly aromaticpolyamides; aliphatic-aromatic polyamides; polyureas; polyurethanefibers, such as those used in “hard” segments of elastomeric AB blockcopolymers (DuPont Spandex technology), in reaction injection molding(RIM) systems for making automobile parts (e.g. bumpers), and in rigidand flexible foams (such as HYPOL™ available from W. R. Grace & Co.(USA)); polyhydrazides; polyimides, such aspoly(4,4′-oxydiphenylene-pyromellitimide) (DuPont KAPTON™);polyaspartimide; polyimidesulfones; polysulfonamides;polyphosphonamides; and proteins, such as wool, silk, collagen,recombinant human collagen, gelatin and regenerated protein.

7. Other polymers used in engineering plastics, including, for example,polyethers such as poly(ethylene oxide) (PEO), poly(ethylene glycol),polytetrahydrofuran or other polyethers used, for instance, in “soft”segments of elastomeric AB block copolymers (DuPont Spandex technology),polyoxymethylene (acetal), poly(phenylene oxide) (PPO),poly(hexafluoropropylene oxide), poly[3,3-(dichloromethyl)trimethyleneoxide], polytetrahydrofuran, polyetherketones (PEK),polyetherketoneketones (PEKK), polyetheretherketones (PEEK),polyetherketoneether ketoneketones (PEKEKK), polyetherimides (PEI);polyethersulfones (PES) such as VICTREX available from ICI; polysulfones(PSU) such as ASTREL™ available from 3M; polysupersulfones (PSS);polybenzimidazoles (PBI); polysulfides such as poly(p-phenylene sulfide)(PPS) and poly(alkylene polysulfides) (known as Thiokol rubbers); andthermoplastic elastomers such as polyether block amides (PEBAX™).

8. Polymers used in thermosetting plastics, laminates and adhesives,including, for example, phenol-formaldehydes (often referred to asphenolic resins), chemically modified phenolic resins optionallycontaining furfural, 5-hydroxymethylfurfural, acrolein, acetaldehyde,butyraldehyde, resorcinol, bisphenol A, o- or p-cresol, o- orp-chlorophenol, p-t-butylphenol, p-phenylphenol, p-n-octylphenol,unsaturated phenols derived from cashew nut shell liquid (such ascardanol), unsaturated phenols from tung oil (such as α-eleostearicacid), 2-allylphenol, naturally occurring phenols such as hydrolyzabletannins (pyrogallol, ellagic acid, glucose esters or condensed forms ofgallic acid), condensed tannins (flavonoid units linked together withcarbohydrates) and lignin; phosphate esterified phonolic resins; furanresins; bisphenol A-furfural resins; unsaturated polyesters; polyetherepoxy resins; amino resins such as urea-formaldehydes andmelamine-formaldehydes (FORMICA™ and BASOFIL™); resoles; novolacs;crosslinked novolacs (e.g. KYNOL™); epoxy cresol novolacs, and epoxyphenol novalacs.

9. Polymers and copolymers used in synthetic elastomers, including, forexample, poly(acrylonitrile-butadiene); poly(styrene-butadiene) (SBR),poly(styrene-butadiene) block and star copolymers;poly(styrene-acrlyonitrile) (SAN), poly(styrene-maleic anhydride) (SMA),poly(styrene-methylmethacrylate); poly(acrylonitrile-butadiene-styrene)(ABS); poly(acrylonitrile-chlorinated polyethylene-styrene);poly(acrylonitrile-butadiene-acrylate); polybutadiene, specifically thecis-1,4 polymer; ethylene-propylene-diene-monomer (EPDM); neoprenerubbers, such as cis or trans-1,4-polychloroprene and1,2-polychloroprene; cis or trans-1,4-polyisoprene;poly(isobutylene-isoprene); poly(isobutylene-cyclopentadiene);poly(1-octenylene)(polyoctenamer);poly(1,3-cyclo-pentenylenevinylene)(norbornene polymer).

10. Other natural polymers, including, for example, natural rubbers suchas hevea(cis-1,4-polyisoprene), guayule(cis-1,4-polyisoprene), gutapercha(trans-1,4-polyisoprene), balata(trans-1,4-polyisoprene) andchicle(cis and trans-1,4-polyisoprene); lignin; humus; shellac; amber;Tall oil derived polymers (rosin); asphaltenes (bitumens);polysaccharides, such as native cellulose derived from seed hair fibers(cotton, kapok, coir), bast fibers (flax, hemp, jute, ramie) and leaffibers (manila hemp, sisal hemp); regenerated cellulose such as viscoserayon and cellophane; derivatives of cellulose including the nitrate(e.g. CELLULOID™), acetate (fibers of which are known as celluloserayon), propionate, methacrylate, crotonate and butylate esters ofcellulose; acetate-propionate and acetate-butyrate esters of cellulose,and mixtures thereof, the methyl, ethyl, carboxymethyl, aminoethyl,mercaptoethyl, hydroxylethyl, hydroxypropyl and benzyl ether derivativesof cellulose (e.g. “thermoplastic starches”); nitrocellulose; vinyl andnonvinyl graft copolymers of cellulose (e.g. ETHYLOSE™); crosslinkedcellulose; hemicelluloses (amorphous) such as xylan, mannan, araban andgalactans; starch, including amylase and amylopectin; derivatives ofstarch such as allylstarch, hydroxyethylstarch, starch nitrate, starchacetate, vinyl graft copolymers of starch such as stryrenated starch;crosslinked starch made using, for instance, epichlorohydrin; chitin;chitosan; alginic acid polymer; carrageenin; agar; glycogen; dextran;inulin; and natural gums such as gum arabic, gum tragacanth, guar gum,xanthum gum, gellan gum and locust bean gum.

11. Heterocyclic polymers, including, for example, polypyrroles,polypyrazoles, polyfurans, polythiophenes, polycyanurates,polyphthalocyanines, polybenzoxazoles, polybenzothiazoles,polyimidazopyrrolones, poly(1,3,4-oxadiazoles) (POD),poly(1,2,4-triazoles), poly(1,3,4-thiadiazoles), polyhydantoins,poly(parabanic acids) also known aspoly(1,3-imidazolidine-2,4,5-triones), polythiazolines, polyimidines,polybenzoxazinone, polybenzoxazinediones, polyisoindoloquinazolinedione,polytetraazopyrene, polyquinolines, polyanthrazolines,poly(as-triazines).

12. Other organic polymers, including, for example, polyamines such aspolyanilines, Mannich-base polymers; and polyaziridines;polycarbodiimides; polyimines (also called azomethine or Schiff basepolymers); polyamidines; polyisocyanides; azopolymers; polyacetylenes;poly(p-phenylene); poly(o-xylylene); poly(m-xylylene); poly(p-xylylene)and chlorinated poly(p-xylylene) (Union Carbide PARYLENE™); polyketones;Friedel-Crafts polymers; Diels-Alder polymers; aliphatic and aromaticpolyanhydrides; ionens; ionene-polyether-ionene ABA block copolymers;halatopolymers; and synthetic bioabsorbable polymers, for example,polyesters/polyactones such as polymers of polyglycolic acid, glycolide,lactic acid, lactide, dioxanone, trimethylene carbonate, polyanhydrides,polyesteramides, polyortheoesters, polyphosphazenes, and copolymers ofthese and related polymers.

13. Inorganic polymers, including, for example, polysiloxanes,polysilanes, polyphosphazines, carborane polymers,ploycarboranesiloxanes (DEXSIL™ and UCARSIL™), poly(sulfur nitride),polymeric sulfur, polymeric selenium, polymeric tellurium, boron nitridefibers, poly(vinyl metallocenes) of ferrocene and ruthenocene,polyesters and polyamides containing metallocenes in the polymerbackbone, poly(ferrocenylsilane); poly(ferrocenylethylene);organometallic vinyl polymers containing manganese, palladium or tin,and copolymers of the former with poly(methyl methacrylate), which areused in biocidal paints for marine applications such as ship hulls andoff-shore drilling platforms; metal-containing polyesters andpolyamides; polymeric nickel(o)-cyclooctatetraene, polymericnorbornadiene-silver nitrate; arylethynyl copper polymers; coordinationpolymers, such as polymers resulting from the reaction ofbis(1,2-dioxime) with nickel acetate, phthalocyanine-type polymers,network transition metal polyphthalocyanines linked through imide orbenzimidazole groups, cofacially linked polyphthalocyanines, ligandexchange polymers resulting from the reaction of bis(β-diketone) andmetal acetylacetonates or tetrabutyl titanate, polymers resulting fromthe reaction of bis(8-hydroxy-5-quinolyl) derivative, and its thiolanalogs, with metal acetylacetonates; polymeric chelates, such aspolyamides resulting from the reaction of diacid chloride withthiopicolinamides, and vinyl polymers containing pendant crown ethers,such as poly(4′-vinylbenzo-18-crown-6).

Homopolymers, copolymers and blends of the polymers described above mayhave any stereostructure, including syndiotactic, isotactic,hemi-isotactic or atactic. Stereoblock polymers are also included. Thepolymers may be amorphous, crystalline, semicrystalline or mixturesthereof; and possess a range of melt index, preferably from about 0.3 toabout 99. The polymers described above may be further derivatized orfunctionalized (e.g. chlorinated, brominated, fluorinated, sulfonated,chlorosulfonated, saponified, hydroborated, epoxidated) to impart otherfeatures (e.g. physical/chemical, end-group conversion, bio andphotodegradation), or in preparation for subsequent crosslinking, blockand graft copolymerization.

Polyolefins, preferably polyethylene and polypropylene, and vinylpolymers exemplified in the preceding paragraphs can be prepared bydifferent, and especially by the following, methods: a) radicalpolymerization (normally under high pressure and at elevatedtemperature); b) catalytic polymerization using a catalyst that normallycontains one or more than one metal of groups IVb, Vb, VIb or VIII ofthe Periodic Table. These metals usually have one or more than oneligand, typically oxides, halides, alcoholates, esters, ethers, amines,alkyls, alkenyls and/or aryls that may be either π- or σ-coordinated.These metal complexes may be in the free form or fixed on substrates,typically on activated magnesium chloride, titanium(III) chloride,alumina or silicon oxide. These catalysts may be soluble or insoluble inthe polymerization medium. The catalysts can be used by themselves inthe polymerization or further activators may be used, typically metalalkyls, metal hydrides, metal alkyl halides, metal alkyl oxides or metalalkyloxanes, said metals being elements of groups Ia, IIa and/or IIIa ofthe Periodic Table. The activators may be modified conveniently withfurther ester, ether, amine or silyl ether groups. These catalystsystems are usually termed Phillips, Standard Oil Indiana, Ziegler(-Natta), TNZ (DuPont), metallocene or single site catalysts (SSC).

Polyesters for use in the invention may be manufactured by any knownsynthetic method, including, for example, direct esterification,transesterification, acidolysis, the reaction of alcohols with acylchlorides or anhydrides, the reaction of carboxylic acids with epoxidesor alkylhalides, and by ring-opening reactions of cyclic esters.Copolyesters, copolymers containing a polyester, and polymer blends,such as engineering plastics comprising polyblends of polycarbonate withPBT or ABS (acrylonitrile-butadiene-styrene) are specificallycontemplated. Solution and interfacial (phase-transfer) methods,catalyzed low temperature and high temperature synthetic methods may beemployed.

Polyamides for use in the invention can be manufactured by any knownmethod, including, for example, solution polymerization, interfacialpolymerization in which an acid chloride and a diamine are used as rawmaterials, by melt polymerization, solid-phase polymerization, or meltextrusion polymerization in which a dicarboxylic acid and a diamine areused as raw materials.

Elastomeric polymers for use in the invention include those genericallyknown as “Spandex” or elastane, preferably comprised of at least 85% byweight of a segmented polyurethane, available commercially under variousbrand name trademarks, including LYCRA™, ELASPAN™, DORLASTAN™ andLINEL™. Spandex fibers are composed of numerous polymer strands that aremade up of two types of segments: long, amorphous “soft” segments andshort, rigid “hard” segments. The spandex polymer back-bone is formed byreacting two prepolymer solutions. The long, amorphous segments consistof a flexible macro-glycol (polyol), such that terminal hydroxyl groupsare present. A common first step is reaction of the macro-glycol(polyol) with a diisocyanate monomer in a reaction vessel undercarefully selected conditions to form a prepolymer. A typical ratio ofglycol (polyol) to diisocyanate may be 1:2, but the ratio is strictlycontrolled in order to produce fibers with the desired characteristics.A catalyst, such as diazobicyclo[2.2.2]octane, may be employed. Theprepolymer may be further reacted with an equal amount of a diol(resulting in a polyurethane) or a diamine (resulting in apolyurethaneurea), in what is known as the chain extension reaction.

Spandex fibers can be manufactured by four different methods includingmelt extrusion, reaction spinning, solution wet spinning, and solutiondry spinning, the latter being used to produce over 90% of the world'ssupply of spandex fiber. These methods of spandex polymer preparationare well known in the art and are disclosed, in part, in U.S. Pat. Nos.2,929,804; 3,097,192; 3,428,711; 3,533,290 and 3,555,115. In thesolution dry spinning process, the prepolymer solution or the solutionresulting from the chain extension reaction is diluted with a solvent toproduce the spinning solution. The solvent helps make the solutionthinner and more easily handled. It can then be pumped into the fiberproduction cell, a cylindrical spinning cell where it is cured andconverted into fibers. In this cell, the polymer solution is forcedthrough a metal plate, called a spinneret, which has small holesthroughout. This causes the solution to be aligned in strands of liquidpolymer. As the strands pass through the cell, they are heated in thepresence of a nitrogen and solvent gas. These conditions cause theliquid polymer to chemically react and form solid strands. As the fibersexit the cell, solid strands are bundled together to produce the desiredfinal thickness. This is done with a compressed air device that twiststhe fibers together. In reality, each fiber of spandex is made up ofmany smaller individual fibers that adhere to one another due to thenatural stickiness of their surface. As part of the final processingsteps, a finishing agent, such as a metal stearate or another polymersuch as poly(dimethyl-siloxane), may be added to prevent the fibers fromsticking together and aid in textile manufacture. After this treatment,the fibers are transferred through a series of rollers onto a spool. Thespandex fibers may be woven with other fibers such as cotton, nylon orpolyester to produce the fabric that is used in clothing manufacture.

Some macro-glycols (polyols) suitable for use in the long, amorphous“soft segments” of spandex for use in the invention consist ofpolyethers (e.g. poly(ethyleneether)glycol,poly(tetramethyleneether)glycol,poly(tetramethyleneether-co-ethyleneether)glycol, andpoly(tetramethyleneether-co-2-methyltetramethyleneether)glycol),polyester (e.g. poly(2,2-dimethyl-1,3-propane dodecanedioate)glycol,poly(ethylene-co-1,2-propylene adipate)glycol,poly(hexamethylene-co-2,2-dimethyltrimethylene adipate)glycol, andpoly(ethylene-co-butylene adipate)glycol), polycarbonates (e.g.poly(pentane-1,5-carbonate)glycol and poly(hexane-1,6-carbonate)glycol),polycaprolactone or some combination of these (e.g. polyesterethers).Some common commercial organic diisocyanates suitable for preparing theshort, rigid “hard segments” of spandex for use in the invention include1-isocyanato-4-[(4-isocyanatophenyl)methyl]benzene (“4,4′-MDI”),1-isocyanato-2-[(4-isocyanatophenyl)methyl]benzene (“2,4′-MDI”),mixtures of 4,4′-MDI and 2,4′-MDI, bis(4-isocyanatocyclohexyl)methane(PICM), 5-isocyanato-1-(isocyanatomethyl)-1,3,3-trimethylcyclohexane,1,3-diisocyanato-4-methyl-benzene, hexamethylene diisocyanate (HMDI),isophorone diisocyanate (IPDI), and α,α,α′,α′-tetramethyl-m-xylylenediisocyanate (mTMXDI), tolylene diisocyanate (TDI), and mixturesthereof, among others.

When a polyurethane spandex is desired, the chain extender utilized inmaking the polymer is a diol, for example ethylene glycol, 1,3-propanediol, and 1,4-butane diol, and mixtures thereof Optionally, amonofunctional alcohol chain terminator such as butanol can be used tocontrol polymer molecular weight, and a higher functional alcohol ‘chainbrancher’ such as pentaerythritol can be used to control viscosity. Theresulting polyurethanes can be melt-spun, dry-spun, or wet-spun intospandex.

When a polyurethaneurea (a sub-class of polyurethanes) spandex isdesired, the chain extender is a diamine, for example ethylene diamine,1,3-butanediamine, 1,4-butanediamine, 1,3-diamino-2,2-dimethylbutane,1,6-hexanediamine, 1,2-propanediamine, 1,3-propanediamine,N-methylaminobis(3-propylamine), 2-methyl-1,5-pentanediamine,1,5-diaminopentane, 1,4-cyclohexanediamine,1,3-diamino-4-methylcyclohexane, 1,3-cyclohexanediamine,1,1′-methylene-bis(4,4′-diaminohexane),3-aminomethyl-3,5,5-trimethylcyclohexane, 1,3-diaminopentane, m-xylylenediamine, and mixtures thereof. Optionally, a chain terminator, forexample diethylamine, cyclohexylamine, or n-hexylamine, can be used tocontrol the molecular weight of the polymer, and a trifunctional ‘chainbrancher’ such as diethylenetriamine can be used to control solutionviscosity. Polyurethaneureas are typically dry-spun or wet-spun intospandex.

Spandex fibers typically contain stabilizing additives to protect theintegrity of the polymer. Hindered phenolic antioxidants are well knownin the art. U.S. Pat. Nos. 4,548,975 and 3,553,290 and JapanesePublished Patent Application JP50-004387 disclose phenolic additivestabilizers for spandex. Some preferred stabilizers for spandex for usein the invention include, for example:1,3,5-tris(4-t-butyl-3-hydroxy-2,6-dimethylbenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)trione[CYANOX™ 1790 sold by Cytec Technology Corp.];1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene[IRGANOX™ 1330 (Ciba) or ETHANOX™ 330 (Albemarle)];1,1-bis(2-methyl-4-hydroxy-5-t-butylphenyl)butane [LOWINOX™ 44B25 (GreatLakes Chemicals)]; 1,1,3-tris(2-methyl-5-t-butyl-4-hydroxyphenyl)butane[LOWINOX™ CA22 (Great Lakes Chemicals)];ethylene-1,2-bis(3-[3-t-butyl-4-hydroxyphenyl]butyrate;ethylene-1,2-bis(3,3-bis[3-t-butyl-4-hydroxyphenyl]butyrate [HOSTANOX™03 (Clariant Corporation)]; a condensation product of p-cresol,dicyclopentadiene and isobutene [WINGSTAY™ L originally sold by GoodyearChemical Co.]; a condensation polymer of p-cresol and divinylbenzene[METHACROL™ 2390, E. I. du Pont de Nemours and Company]; and the like.U.S. Pat. No. 6,846,866 discloses synergies in spandex among stabilizerschosen from: 1) mono-hindered phenols having a molecular weight of atleast about 300 Daltons, 2) a second additive selected from the groupconsisting of i) condensation polymers of p-cresol and divinyl benzeneand ii) compounds comprising at least one unsymmetrically di-hinderedphenol group and having a molecular weight of at least about 300Daltons; and 3) an inorganic chlorine-resist additive selected from thegroup consisting of hydrotalcite, a physical mixture of huntite andhydromagnesite, Periodic Group II and IIb metal compounds selected fromthe group consisting of carbonates, oxides, and hydroxides, and PeriodicGroup II and IIb mixed metal compounds selected from the groupconsisting of carbonates, oxides, and hydroxides. The concentration ofthe phenolic antioxidant in the spandex is usually in the range of 0.05to 5%, preferably 0.5 to 2%, based on the weight of the spandex polymer.U.S. Pat. Nos. 4,340,527 and 5,626,960 disclose inorganic additives(e.g. zinc oxide and hydrotalcite) for spandex, contemplated for use inthe invention.

Conventional methods can be employed for adding a stabilizer or addenda,such as the silver sulfate of this invention, to spandex polymer. Forexample, a concentrated slurry or dispersion of the silver sulfategrains of the invention can be prepared in a compatible solvent,preferably the same solvent as is used to prepare the spandex spinningsolution, and added to the spandex prepolymer solutions prior to formingthe polymer into articles, such as fibers or films. More specifically,silver sulfate grains of the invention may be added to the macro-glycol(polyol) prepolymer solution, the diisocyanate prepolymer solution, thechain extension reaction solutions, the spinning solutions, or added tomore than one or all of these solutions. Alternatively, the silversulfate grains of the invention may be applied to the spandex fibersduring the final processing (finishing and drying) steps. In the case ofmelt extrusion manufacturing methods, silver sulfate grains of theinvention may be added to the spandex by direct mixing or compounding,through blending and mixing of a masterbatch concentrate containing thesilver sulfate grains of the invention, or by a conventional feeder orstuffer device on a twin-screw compounder or the like, as describedpreviously.

U.S. Pat. No. 6,479,144 discloses that spandex fibers prepared by a meltextrusion process to which particles of a silver based antimicrobialagent (e.g. silver zirconium phosphate, silver glass or silver zeolite)were added along with a standard spandex lubricant (KELMAR® 660),imparted the spandex fibers with excellent anti-tack properties. Uniformdistribution as well as a number of non-uniform distributions of thesilver-based antimicrobial agent in a sheath/core structured spandexfiber is disclosed and hereby incorporated in its entirety by reference.

Besides a polymer and silver sulfate, the composite material ormasterbatch of the invention can include any optional addenda. Theseaddenda can include nucleating agents, fillers (including fibrousreinforcing fillers such as glass or graphite fibers, and granularreinforcing filler such as carbon black), plasticizers (includinginternal and external versions, the latter including, for example, thearomatic phthalate esters exemplified by di-2-ethylhexylphthalate, thealiphatic esters such as di-2-ethylhexyladipate,di-2-ethylhexylsebacate, and di-2ethylhexylazelate, epoxy plasticizerssuch as epoxidized linseed oil and epoxidized soya oil, polymericplasticizers such as poly(akylene adipates, sebecates, or azelates),chlorinated paraffins and phosphate esters), surfactants, intercalates,compatibilizers, coupling agents, impact modifiers (such aspolybutadiene copolymer), chain extenders, colorants, lubricants,antistatic agents, pigments and delustrants such as titanium oxide, zincoxide, talc, calcium carbonate, dispersants such as fatty amides (e.g.stearamide), metallic salts of fatty acids (e.g. zinc stearate, calciumstearate or magnesium stearate), dyes such as ultramarine blue, cobaltviolet, antioxidants, odorants, fluorescent whiteners, ultravioletabsorbers (such as hydroxybenzotriazoles (e.g. Tinuvins)), tertiaryamine compounds to protect against air pollutants such as oxides ofnitrogen, fire retardants, including brominated flame retardants such aspentabromodiphenylether, abrasives or roughening agents such asdiatomaceous earth, cross-linking agents, wetting agents, thickeningagents, foaming agents and the like. Specifically contemplated are thehindered phenolic antioxidants and the organic disulfide stabilizers, aswell as the combination of stabilizers as disclosed in U.S. patentapplication Ser. No. 11/669,830 filed Jan. 31, 2007, the disclosure ofwhich is incorporated by reference herein. The use of bromate ion andiodate ion as addenda to inhibit discoloration as disclosed in U.S.patent application Ser. No. 11/694,390 filed Mar. 30, 2007, thedisclosure of which is incorporated by reference herein, is furtherspecifically contemplated. As such it is specifically contemplated toadd salts of bromate ion (such as sodium bromate) and/or iodate ion(such as potassium iodate) either to the preparation of the silver-basedantimicrobial agent (e.g. added before, during or after silver ionaddition during precipitation of silver sulfate) or later duringmelt-processing of the polymer, preferably prior to the addition orcompounding of the silver-based antimicrobial agent. These optionaladdenda and their corresponding amounts can be chosen according to need.Incorporation of these optional addenda in the purge material can beaccomplished by any known method.

Polymer composites of the invention may be fabricated in any knownshape, such as fibers, films or blocks, or injection molded into partsof various shapes. Fibers may be solid or hollow, and either round ornon-round in cross section. The latter may assume ribbon, wedge(triangular) and core (hub & spokes), multilobe (such as trilobe, cross,star and higher multilobe cross sections), elliptical and channeledcross sections (designed to promote moisture wicking, such as inCOOLMAX™ fibers). Bicomponent and multicomponent fiber configurations,such a concentric sheath/core, eccentric sheath/core, side-by-side, piewedge, hollow pie wedge, core pie wedge, three islands andislands-in-the-sea, are specifically contemplated. The silver-basedantimicrobial agents may be added with the intent of being uniformlydistributed throughout the various components of a multicomponent fiber,or may be added with the intent of providing a non-uniform distributionamong the distinct fiber components. For example, the silver-basedantimicrobial agent may be added preferentially, in whole or in part, tothe sheath of a sheath/core bicomponent fiber structure to enhanceantimicrobial efficacy at or near the surface of the bicomponent fiber.Alternatively, inclusion of a substantial portion of the silver-basedantimicrobial in the core region, including a region from the center ofthe fiber outward a specified distance (e.g. one-half, one-third,one-fourth or one-fifth of the radius), of a sheath/core fiber mayenhance the durability of the antimicrobial effect or other features,such as lubricity or cohesion, of the multicomponent fiber. Similarly,it is contemplated to include a substantial portion of the silver-basedantimicrobial agent in the “soft segment” of spandex to, perhaps,enhance antimicrobial efficacy at or near the surfaces of the fiber,while possibly including a portion of the silver-based antimicrobialagent in the “hard segments” of spandex to, perhaps, enhance thedurability of the antimicrobial effect.

Splittable synthetic fibers, such as those spun of at least twodissimilar polymers in either segment-splittable or dissolvable“islands-in-the-sea” formats, are contemplated for use in the invention.Segment splittable fibers are typically spun with 2 to 32 segments in around fiber, although 16 segments in a pie wedge (or “citrus”) crosssection and 8 segments in a hollow or core pie wedge cross section arecommonly used at production scales. Microfibers of 2-4 micron diameter,typically with a wedge shaped cross section, are produced after someenergy input received during subsequent textile processing (e.g.hydro-entanglement, carding, airlaying, wetlaying, needlepunching)causes the segments to separate. Segmented ribbon and segmentedmultilobe (e.g. segmented cross and tipped trilobe) cross sections offerenhanced fiber splittability, but the cost of spinnerets capable offorming these cross section shapes is high. Splittable segmentedbicomponent fibers of nylon/polyester are commercially available (e.g.DUOTEX™ and STARFIBER™). Other polymer combinations used in splittablebicomponent fibers include polypropylene/nylon, polypropylene/polyester,polypropylene/poly(acrylonitrile), polypropylene/polyurethane,all-polyester splittable fibers made from poly(lactic acid)/PET, andall-polyolefin splittable fibers made from polypropylene/poly(methylpentene).

Splittable fiber technology as originally disclosed in U.S. Pat. No.3,705,226 employed an “islands-in-the-sea” format in which a staplefiber was spun with extremely fine diameter PET fibers surrounded by adissolvable “sea” of copolymer. Suitable dissolving polymers includepolystyrene (soluble in organic solvents), poly(lactic acid), polyvinylalcohol, thermoplastic starches and other co-polyesters soluble in hotwater. Nylon microfibers of about 6 micron diameter have been producedcommercially from a fiber originally containing 37 islands of Nylon 6 inan alkali-soluble copolyester sea. Island/sea fibers with up to 600islands have yielded microfibers about 1 micron in diameter.

Silver sulfate particles precipitated in accordance with the inventioncan be incorporated within plastics, polymers and polymer containingmaterials to provide antimicrobial (antibacterial and/or antifungal) orantiviral protection in a variety of end-use applications. Typicalend-use applications include, but are not limited to, extruded andnon-extruded face fibers for carpets and area rugs (e.g. rugs withpolypropylene face fibers (such as commercial, retail or residentialcarpet); carpet backing (either primary or secondary backing, comprisingwoven or nonwoven polypropylene fibers), or the latex adhesive backingsused in carpet (commercial, residential or retail)). In addition,antimicrobial-incorporated and antiviral-incorporated polymers may alsobe used in liquid filtration media (such as non-woven filtration mediafor pools and spas, waste water treatment, potable water treatment, andindustrial applications such as metalworking); non-woven air filtrationmedia (such as commercial and residential furnace, HVAC or humiditycontrol filters, air purifiers, and HEPA filters, and cabin air filtersfor automobiles and airplanes). Further, antimicrobial-incorporatedpolymers can be used for outdoor fabrics (such as woven and non-wovencar and boat covers, tarps, tents, canvas, sails, ropes, pool covers,patio upholstery (such as umbrellas, awnings, seating), camping gear andgeotextiles), building materials (such as drywall, weather stripping,insulation, housewrap and roof wrap, wall paper, flooring materials suchas cement, concrete, mortar and tile, synthetic marble for kitchen andbath counters and sinks, sanitary ceramics, toilets, shower stalls andcurtains, sealing materials (such as latex paint and organic solventbased paints/stains and exterior weather-proofing stains, adhesives forplumbing and packaging, glazing for windows, tile and vitreous china,grout), push buttons for elevators, handrails for stairs, mats, andknobs), industrial equipment (such as tape, tubing, barrier fabrics,conveyor belts, insulators and insulation for wire and cable, plumbingsupplies and fixtures, gaskets, collection and storage equipment(including piping systems, silos, tanks and processing vessels) andcoatings used on the inside of fire system sprinkler pipes), dailynecessities (such as chopping boards, disposable gloves, bowls, kitchendrain baskets, kitchen refuse baskets, kitchen knife handles,chopsticks, tableware, table cloths, napkins, trays, containers, lunchboxes, chopstick cases, dusters, sponges, brooms, mops, wipes, bathroomstools, washbowls, pales, cupboards, soap cases, shampoo holders,toothbrush holders, toothbrushes, dental floss, razor blade handles,wrapping films, food wraps and packaging, canteens, emergency watertanks, toilet seats, hairbrushes, combs, scrubbers, tools and toolhandles, cosmetics and cosmetic containers, and clothing). Other usesenvisioned include incorporation the materials of the invention intostationary and writing materials (such as mechanical pencils, ball-pointpens, pencils, erasers, floppy disk cases, clipboards, clear paperholders, fancy cases, video tape cases, photo-magnetic disk shells,compact disk cases, desk mats, binders, book covers, writing paper andpocket books), automobile parts (such as a steering wheels, armrests,panels, shift knobs, switches, keys, door knobs, assist grips),appliances (such as refrigerators, washing machines, vacuum cleaners andbags, air conditioners, clothing irons, humidifiers, dehumidifiers,water cleaners, dish washers and dryers, rice cookers, stationary andmobile telephones, copiers, touch panels for ATM or retail kiosks (e.g.photo-kiosks, etc.)), textile products (such as socks, leggings, hosiery(such as pantyhose, surgical hose, support hose), undergarments(including brassieres, brassiere straps and bra side panels), foundationgarments, inner liners for jackets, gloves and helmets, bathing suits,body and motion capture suits, towels, toilet covers, curtains, carpetfibers, pillows, sheets, bedclothes, mattress ticking, sleeping bags,nose and mouth masks, towels, caps, hats, wigs, etc.) goods related topublic transportation (such as overhead straps, handles and grips,levers, seats, seat belts, luggage and storage racks) sporting goods(such as balls, nets, pucks, whistles, mouth pieces, racket handles,performance clothing, such as cycling shorts, protective gear, helmets,indoor and outdoor artificial turf, shoe linings and reinforcements,tools, structures and ceremonial objects used in athletic events and themartial arts), medical applications (such as bandages, gauze, catheters,artificial limbs, implants, instruments, scrubs, facemasks, shields,reusable and disposable diapers, sanitary napkins, tampons, condoms,uniforms, gowns and other hospital garments requiring aggressive andharsh cleaning treatments to allow the garment to be safely worm by morethan one person). Miscellaneous applications for the invention furtherinvolve inclusion in musical instruments (such as in reeds, strings andmouthpieces), contact lens, lens keepers and holders, plasticcredit/debit cards, sand-like materials for play boxes, cat and petlitter, jewelry and wrist watch bands.

Application of the antimicrobial agents of the invention for medicaluses is specifically contemplated, and formulations may be incorporatedin a variety of formats:

-   -   1. Coatings of the antimicrobial agent on medical grade        substrates, for example, dressings, packings, meshes, films,        filtering surfaces, filters, infusers, fibers such as dental        floss or sutures, containers or vials, from materials composed        of, for example, polyethylene, high density polyethylene,        polyvinylchloride, latex, silicone, cotton, rayon, polyester,        nylon, cellulose, acetate, carboxymethylcellulose, alginate,        chitin, chitosan and hydrofibers;    -   2. Powders (i.e. as free standing powders) of the antimicrobial        agent, or as coatings of the antimicrobial agent on        biocompatible substrates in powder form, preferably on        hydrocolloids, bioabsorbable and/or hygroscopic substrates such        as:        -   Synthetic Bioabsorbable Polymers: for example,            polyesters/polyactones such as polymers of polyglycolic            acid, glycolide, lactic acid, lactide, dioxanone,            trimethylene carbonate, polyanhydrides, polyesteramides,            polyortheoesters, polyphosphazenes, and copolymers of these            and related polymers or monomers, or        -   Naturally Derived Polymers:            -   Proteins: albumin, fibrin, collagen, elastin;            -   Polysaccharides: chitosan, alginates, hyaluronic acid;                and            -   Biosynthetic Polyesters: 3-hydroxybutyrate polymers;    -   3. Occlusions or hydrated dressings, in which the dressing is        impregnated with a powder or solution of the antimicrobial        agent, or is used with a topical formulation of the        antimicrobial agent, with such dressings for example as        hydrocolloids, hydrogels, polyethylene, polyurethane,        polvinylidine, siloxane or silicone dressings;    -   4. Gels, formulated with powders or solutions of the        antimicrobial agent with such materials as hydrocolloid powders        such as carboxymethylcellulose, alginate, chitin, chitosan and        hydrofibers, together with such ingredients as preservatives,        pectin and viscosity enhancers;    -   5. Creams, lotions, pastes, foams and ointments formulated with        powders or solutions of the antimicrobial agent, for example as        emulsions or with drying emollients;    -   6. Liquids, formulated as solutions, dispersions, or        suspensions, by dissolving coatings or powders of the        antimicrobial agent, for example as topical solutions, aerosols,        mists, sprays, drops, infusions and instillation solutions for        body cavities and tubes such as the bladder, prostate,        perintheal, pericharcliar, pleural, intestinal and ailimentary        canal;    -   7. Formulations suitable for administration to the nasal        membranes, the oral cavity or to the gastrointestinal tract,        formulated with powders or liquids of the antimicrobial or noble        metal in such forms as lozenges, toothpastes, gels, powders,        coated dental implants, dental floss or tape, chewing gum,        wafers, mouth washes or rinses, drops, sprays, elixirs, syrups,        tablets, or capsules;    -   8. Formulations suitable for vaginal or rectal administration        formulated with powders or liquids of the antimicrobial agent in        such forms as suppositories, dressings, packings, tampons,        creams, gels, ointments, pastes, foams, sprays, and solutions        for retention enemas or instillations.

Some specific medical end-use applications in which the invention iscontemplated for use include, for example:

-   -   1. Absorbing and non-absorbing suture materials, formed as        monofilament or as braided or twisted multifilaments, employing        materials such as silk, polyester, nylon, polypropylene,        polyvinylidenefluoride, linen, steel wire, catgut (beef serosa        or ovine submucosa), polyglycolactide, polyamide (e.g. polyamide        nylon), fibroin, polyglycolic acid and copolymers thereof, such        as, for example, a polyglycolide (or polyglycolic        acid)/polycaprolactone co-polymer or a polyglycolic        acid/polycaprolactam co-polymer);    -   2. Surgical adhesives and sealants, including, for example,        cyanoacrylates, such as butyl-4-cyanoacrylate and the polymer        2-octyl cyanoacrylate (DERMABOND™); polyethylene glycol        hydrogels, such as COSEAL™ (Baxter Healthcare Corporation (USA))        and DuraSeal Dural (Confluent Surgical, (USA)), purified bovine        serum albumin (BSA) and glutaraldehyde, such as BIOGLUE™        (Cryolife, Inc.(USA)); fibrins, such as CROSSEAL™ (Ethicon, Inc.        (USA)) and TISSEAL™; microfibrillar collagens, such as AVITENE™        flour, ENDOAVITENE™ preloaded applications, and SYRINGEAVITENE™        (Davol, Inc. (USA)); resorbable collagens, such as BIOBLANKET™        (Kensey Nash (USA)); recombinant human collagens; phase inverted        biopolymers, such as POLIPHASE™ (Avalon Medical, Ltd.);        fibrinogen and thrombin, such as HEMASEEL™ APR (Haemacure        Corporation (Canada)), and FIBRX™ (Cryolife, Inc. (USA));        autologous processed plasma, such as ATELES™, CEBUS™, and        PROTEUS™ (PlasmaSeal (USA)); polyethylene and polyurethane        adhesive foams, such as those from Scapa Medical; rubber-based        medical adhesives (Scapa Medical); aesthetic injectable        adhesives, such as BIOHESIVE™ (Bone Solutions, Inc (USA); and        others, including BAND-AID™ Brand Liquid Bandage Skin Crack Gel,        THOREX™ from Surgical Sealants, Inc. (USA); and “aliphatic        polyester macromers” as disclosed in US20060253094;    -   3. Primary wound dressings, for example, TEGADERM™ Ag Mesh,        TEGADERM™ Ag Mesh With Silver, TEGADERM™ HI and HG Alginate        Dressings, TEGADERM™ Hydrogel Wound Filler, TEGADERM™ Foam        Adhesive and Non-Adhesive Dressings, COBAN™ Self-Adherent Wrap,        CAVILON™ No-Sting Barrier Film, available from 3M (USA);    -   4. Surgical closure tape, such as STERI-STRIP™ S Surgical Skin        Closure Tape and MEDIPORE™ H Soft Cloth Surgical Tape from 3M        (USA);    -   5. Hemostats, in the form of topical applications, such as        various forms of thrombin; matrix applications, such as bovine        thrombin with cross-linked gelatin granules (FLOSEAL™ from        Baxter International); sheets, such as AVITENE™ microfibrillar        collagen from Davol, Inc. (USA); gauze, such as BLOODSTOP™ and        BLOODSTOP™ iX (LifesciencePlus (USA)), and ActCel (ActSys        Medical (USA)); gelatin sponge, such as GELFOAM™; collagen        sponge, such as ULTRAFOAM™ (Davol, Inc. (USA)); lyophilized        collagen sponge, such as INSTAT™ (Ethicon, Inc. (USA)); and        oxidized regenerated cellulose, such as OXYCEL™ and SURGICEL™        (Ethicon, Inc. (USA))

6. Dental pit and fissure sealants, and luting cements.

Application of the materials of this invention in polymer-woodcomposites is also contemplated. With the rising cost of wood and theshortage of mature trees, there is a need to find good qualitysubstitutes for wood that are more durable and longer-lasting (lesssusceptible to termite destruction and wood rot). Over the past severalyears, a growing market has emerged for the use of polymer-woodcomposites to replace traditional solid wood products in end-useapplications such as extruded and foam-filled extruded building andconstruction materials (such as window frames, exterior cladding,exterior siding, door frames, ducting, roof shingles and relatedroofline products, and exterior boardwalks and walkways); interiors andinternal finishes (for example, interior paneling, decorative profiles,office furniture, kitchen cabinets, shelving, worktops, blinds andshutters, skirting boards, and interior railings); automotive (includingdoor and head liners, ducting, interior panels, dashboards, rearshelves, trunk floors, and spare tire covers); garden and outdoorproducts (such as decking, fence posts and fencing, rails and railings,garden furniture, sheds and shelters, park benches, playgroundequipment, and playground surfaces); and finally, industrialapplications (including industrial flooring, railings, marine pilings,marine bulkheads, fishing nets, railroad ties, pallets, etc.).Polymer-wood composites also offer anti-sapstain protection.

Polymer-wood composites may vary widely in composition, with polymercontent typically ranging from about 3-80% by weight depending onend-use. Injection molded products require adequate flow of the moltenmaterial; and therefore, preferably contain from about 65 to 80% byweight of the polymer component. Whereas composites requiring structuralstrength may typically contain only about 3-20% polymer by weight, thepolymer typically serving primarily as an adhesive. Perhaps the mostcommonly employed polymer components are the polyolefins (polyethyleneor polypropylene, high density and low density versions and mixturesthereof), although polybutene, polystyrene, and other polymers withmelting temperatures between about 130°-200° C. are also used. Inprincipal, any polymer with a melt temperature below the decompositiontemperature of the cellulosic fiber component may be employed.Crosslinking chemicals (such as peroxides and vinylsilanes),compatibilizers and coupling agents (such as grafted-maleic anhydridepolymers or copolymers) that incorporate functionality capable offorming covalent bonds within or between the polymer and cellulosiccomponents may be included. Cellulosic materials can be obtained from awide variety of sources: wood and wood products, such as wood pulpfibers; non-woody paper-making fibers from cotton; straws and grasses,such as rice and esparto; canes and reeds, such as bagasse; bamboos;stalks with bast fibers, such as jute, flax, kenaf, linen and ramie; andleaf fibers, such as abaca and sisal; paper or polymer-coated paperincluding recycled paper and polymer-coated paper. One or morecellulosic materials can be used. More commonly, the cellulosic materialused is from a wood source. Suitable wood sources include softwoodsources such as pines, spruces, and firs, and hardwood sources such asoaks, maples, eucalyptuses, poplars, beeches, and aspens. The form ofthe cellulosic materials from wood sources can be sawdust, wood chips,wood flour, or the like. Still, microbes such as bacteria and fungus canfeed on plasticizers or other additives and environmental foodstuffsfound in or on the polymer component, resulting in discoloration andstructural (chemical or mechanical) degradation. The present inventionprovides a means to more effectively address these issues byincorporating antimicrobial or antiviral agents in either or both of thepolymer and wood components of these composites.

Another emerging application to which the present invention isparticularly applicable is antimicrobial nonwoven fabrics, textiles thatare neither woven nor knit. Nonwoven fabric is typically manufactured byputting small fibers together in the form of a sheet or web, and thenbinding them either mechanically (as in the case of felt, byinterlocking them with serrated needles such that the inter-fiberfriction results in a stronger fabric), with an adhesive, or thermally(by applying binder (in the form of powder, paste, or polymer melt) andmelting the binder onto the web by increasing the temperature, or bythermal spot bonding). Nonwovens are often classified as either durableor single-use (disposable), depending on the end-use application.

Staple nonwovens are made in two steps. Fibers are first spun, cut to afew centimeters length, and put into bales. These bales are thendispersed on a conveyor belt, and the fibers are spread in a uniform webby a wetlaid process or by carding. Wetlaid operations typically use ¼″to ¾″ long fibers, but sometimes longer if the fiber is stiff or thick.Carding operations typically use ˜1.5″ long fibers. Fiberglass may bewetlaid into mats for use in roofing and shingles. Synthetic fiberblends are wetlaid along with cellulose for single-use fabrics. Staplenonwovens are bonded throughout the web by resin saturation or overallthermal bonding or in a distinct pattern via resin printing or thermalspot bonding. Coforming with staple fibers usually refers to acombination with meltblown, often used in high-end textile insulations.

Spunlaid nonwovens are made in one continuous process. Fibers are spunand then directly dispersed into a web by deflectors or directed withair streams. This technique leads to faster belt speeds, and lower cost.Several variants of this concept are commercially available, a leadingtechnology is the Reicofil machinery, manufactured by Reifenhäuser(Germany). In addition, spunbond has been combined with meltblownnonwovens, coforming them into a layered product called SMS(spun-melt-spun). Meltblown nonwovens have extremely fine fiberdiameters but are not strong fabrics. SMS fabrics, made completely frompolypropylene are water-repellent and fine enough to serve as disposablefabrics. Meltblown nonwovens are often used as filter media, being ableto capture very fine particles.

In other processes, nonwovens may start from films and fibrillate,serrate or vacuum-formed shapes made with patterned holes. The spunlaceprocess achieves mechanical intertwining of the nonwoven fibers by theuse water jets (hydro-entanglement). Ultrasonic pattern bonding is oftenused in high-loft or fabric insulation/quilts/bedding. In an unusualprocess, nonwoven housewrap (e.g. DuPont TYVEK™) utilizes polyethylenefibrils in a Freon-like fluid, forming and calendering them into apaper-like product; while spunbound polypropylene (e.g. DuPont TYPAR™)is used in carpet backing, packaging, construction (roof and housewrap)and geotextile applications.

Fiberglass nonwovens are of two basic types. Wet laid mat or “glasstissue” use wet-chopped, heavy denier fibers in the 6 to 20 micrometerdiameter range. Flame attenuated mats or “batts” use discontinuous finedenier fibers in the 0.1 to 6 micron range. The latter is similar,though run at much higher temperatures, to meltblown thermoplasticnonwovens. Wet laid mat is almost always wet resin bonded with a curtaincoater, whereas batts are usually spray bonded with wet or dry resin.

The use of natural fibers such as cellulose in nonwovens (e.g. nonwovencotton mesh gauze available as TEGADERM™, and nonwoven rayon availableas BEMLIESE™) has largely given way to man-made fibers such as thepolyolefins and polyester (mostly PET). PET-based nonwovens are superiorin resiliency, wrinkle recovery and comfort when in contact with theskin, as well as in high temperature performance. Applications forpolyester (as well as polyethylene and polypropylene) nonwovens includemedical (such as isolation caps, gowns, covers and masks; surgicaldrapes, gowns and scrub suits) hygiene (baby diapers, feminine hygiene,adult incontinence products, wipes, bandages and wound dressings),filters (gasoline, oil and air—including HEPA filtration, water, pooland spa, coffee and tea bags) geotextiles (soil stabilizers and roadwayunderlayment, agricultural mulch, pond and canal barriers, and sandfiltration barriers for drainage tiles) technical (ceiling tile facings,circuit board reinforcement, electrical insulation, insulation backing,honeycomb structural components, roll roofing and shingle reinforcement,wall coverings, vinyl flooring reinforcement and plastic surfacereinforcement (veils)) and miscelaneous (carpet backing, marine sail andtabletop laminates, backing/stabilizer for machine embroidery,filberglass batting insulation, pillows, cushions and upholsterypadding, and batting in quilts or comforters).). Commercial offeringsuseful for wound dressings include, for example, perforated,non-adherent non-woven meshes such as; DELNET™ P530, which is anon-woven veil formed of high density polyethylene using extrusion,embossing and orientation processes, produced by Applied ExtrusionTechnologies, Inc. of Middletown, Del., USA. This same product isavailable as Exu-Dry CONFORMANT 2™ wound veil, from Frass SurvivalSystems. Inc., Bronx, N.Y., USA as a subset of that company's WoundDressing Roll (Non-Adherent) products. Other useful non-woven meshesinclude CARELLE™ available from Carolina Formed Fabrics Corp., USA, andN-TERFACE™ available from Winfield Laboratories, Inc., of Richardson,Tex., USA.

Nylon is also excellent in high temperature applications, but its use innonwovens is more limited due to its high cost relative to rayon,polyolefins and polyesters; and reduced comfort relative to polyesterswhen used as a textile. Nonetheless, nylon is used as a blending fiberin athletic wear, nonwoven garment linings and in wipes because itimparts excellent tear strength(commercial offerings include, forexample, NYLON 90™ available from Carolina Formed Fabrics Corporation(USA)). Nylon is often used in surface conditioning abrasives whereinabrasive grains are adhered with resin to the internal fiber surfaces ofa nonwoven nylon backing/support. Tools containing such anabrasive/nylon system take the form of nonwoven pads, nonwoven wheels,nonwoven sheets & rolls, surface conditioning discs, convolute wheels,unified or unitized wheels and flap nonwoven wheels. Nonwoven nylon isalso used as an electrode separator in Ni/H and Ni/Cd batteries. Anunusual specialty spunbond nylon (CEREX™) is self-bonded by a gas-phaseacidification process.

Nonwoven substrates composed of multiple fiber types, including bothnatural and synthetic fiber materials, may be used in the presentinvention. Commercial offerings of such blended nonwoven layer materialshave included SONTARA® 8868, a hydro-entangled material, containingabout 50/50 cellulose/polyester, and SONTARA™ 8411, a 70/30rayon/polyester blend commercially available from Dupont Canada,Mississauga, Ontario, Canada; HFE-40-047, an apertured hydro-entangledmaterial containing about 50% rayon and 50% polyester; and NOVENET®149-191, a thermo-bonded grid patterned material containing about 69%rayon, about 25% polypropylene, and about 6% cotton, both of the latterfrom Veratec, Inc., Walpole, Mass. (USA); and KEYBAK® 951V, a dry formedapertured material, containing about 75% rayon and about 25% acrylicfibers from Chicopee Corporation, New Brunswick, N.J. (USA).

In contrast to staple nonwoven fabrics that employ short fibers of onlya few centimeters in length, continuous filament nonwoven fabrics areformed by supplying a low viscosity molten polymer that is then extrudedunder pressure through a large number of micro-orifices in a plate knownas a spinneret or die, which creates a plurality of continuous polymericfilaments. The filaments are then quenched and drawn, and collected toform a nonwoven web. Extrusion of melt polymers through micro-orificesrequires that polymer additives have particle sizes significantlysmaller than the orifice diameter. It is preferred that the additiveparticles be less than a quarter of the diameter of the orifice holes toavoid process instabilities such as filament breakage and entanglement,or “roping”, of filaments while still in the molten state.Microfilaments may typically be on the order of about 20 microns indiameter, while super microfilaments may be on the order of 3-5 micronsor less. Continuous filament nonwoven fabrics formed from supermicrofilaments are mainly used in air filters, as well as in artificialleathers and wipes. Commercial processes are well known in the art forproducing continuous microfilament nonwoven fabrics of many polymers(e.g. polyethylene, polypropylene, polyester, rayon, polyvinyl acetate,acrylics, nylon). Splittable microfibers of 2-3 micron or less diameterare readily processable on nonwoven textile equipment (carded, airlaid,wetlaid, needlepunch and hydro-entanglement). As demonstrated in theexamples below, the present invention enables production of stablesilver sulfate particles having mean grain-sizes of less than 70micrometers, and accordingly, may then be more efficiently incorporatedinto fine diameter monofilaments.

The following examples are intended to demonstrate, but not to limit,the invention.

EXAMPLES

Particle size measurements were performed on the silver sulfatematerials of the examples described below using equilibrated aqueousdispersions of the particles in a Horiba LS-920 Analyzer describedabove. The particle size characterizations of the materials precipitatedin Examples 1-18 are summarized in Tables 1-4 below. The amount of theadditive is expressed as a weight in grams and as a molar percentrelative to the moles of silver added to the reactor.

Examples 1-7

Examples 1-7 illustrate monocarboxylic acid additives or salts thereofof the invention.

Example 1 Comparative, No Additive

A six-liter stainless steel sponge kettle was charged with 2L ofdistilled water and the temperature controlled at 40° C. A planar mixingdevice previously described (Research Disclosure 38213, February 1996 pp111-114 “Mixer for Improved Control Over Reaction Environment”)operating at 3000 rpm was used to ensure the homogeneity of the reactorcontents. To this reactor 71.2 mL of a 3.6M solution of ammonium sulfatewas added. Peristaltic pumps were used to simultaneously deliver a 640mL solution containing 3.1M silver nitrate at a rate of 225.0 mL/min anda 333 mL solution containing 2.9M ammonium sulfate at a rate of 117.1mL/min causing precipitation of a white product. The reaction was heldat 40° C. for 5 min. The final product was washed to a conductivity of<10 mS and a portion was dried at ambient temperature. Powder X-raydiffraction confirmed the product was single-phase silver sulfate. Themean grain size was determined by light scattering (HORIBA) to be 76 μm.Optical micrographs of dried product indicated a mean grain sizeconsistent with that found from the light scattering measurement.

Example 2 Comparative, Ethanol (2g) Added with Silver

A six-liter stainless steel sponge kettle was charged with 2L ofdistilled water and the temperature controlled at 40° C. The reactorcontents were mixed as described in Example 1. To this reactor 71.2 mLof a 3.6M solution of ammonium sulfate was added. Peristaltic pumps wereused to simultaneously deliver a 640 mL solution containing 3.1M silvernitrate at a rate of 225.0 mL/min, a 333 mL solution containing 2.9Mammonium sulfate at a rate of 117.1 mL/min and a 67 mL solutioncontaining 2 g of ethanol at a rate of 23.3 mL/min causing precipitationof a white product. The reaction was held at 40° C. for 5 min. The finalproduct was washed to a conductivity of <10 mS and a portion was driedat ambient temperature. The mean grain size was determined by lightscattering (HORIBA) to be 89 μm.

Example 3 Comparative, Ammonium Acetate (0.5 g) Added with Silver

A six-liter stainless steel sponge kettle was charged with 2L ofdistilled water and the temperature controlled at 40° C. The reactorcontents were mixed as described in Example 1. To this reactor 71.2 mLof a 3.6M solution of ammonium sulfate was added. Peristaltic pumps wereused to simultaneously deliver a 640 mL solution containing 3.1M silvernitrate at a rate of 225.0 mL/min, a 333 mL solution containing 2.9Mammonium sulfate at a rate of 117.1 mL/min and a 67 mL solutioncontaining 0.5 g of dissolved ammonium acetate at a rate of 23.3 mL/mincausing precipitation of a white product. The reaction was held at 40°C. for 5 min. The final product was washed to a conductivity of <10 mSand a portion was dried at ambient temperature. The mean grain size wasdetermined by light scattering (HORIBA) to be 86 μm.

Example 4 Inventive, Ammonium Acetate (2 g) Added with Silver

A six-liter stainless steel sponge kettle was charged with 2L ofdistilled water and the temperature controlled at 40° C. The reactorcontents were mixed as described in Example 1. To this reactor 71.2 mLof a 3.6M solution of ammonium sulfate was added. Peristaltic pumps wereused to simultaneously deliver a 640 mL solution containing 3.1M silvernitrate at a rate of 225.0 mL/min, a 333 mL solution containing 2.9Mammonium sulfate at a rate of 117.1 mL/min and a 67 mL solutioncontaining 2 g of dissolved ammonium acetate at a rate of 23.3 mL/mincausing precipitation of a white product. The reaction was held at 40°C. for 5 min. The final product was washed to a conductivity of <10 mSand a portion was dried at ambient temperature. The mean grain size wasdetermined by light scattering (HORIBA) to be 58 μm. Optical micrographsof dried product indicated a mean grain size consistent with that foundfrom the light scattering measurement.

Example 5 Inventive, Potassium Formate (2 g) Added with Silver

A six-liter stainless steel sponge kettle was charged with 2L ofdistilled water and the temperature controlled at 40° C. The reactorcontents were mixed as described in Example 1. To this reactor 71.2 mLof a 3.6M solution of ammonium sulfate was added. Peristaltic pumps wereused to simultaneously deliver a 640 mL solution containing 3.1M silvernitrate at a rate of 225.0 mL/min, a 333 mL solution containing 2.9Mammonium sulfate at a rate of 117.1 mL/min and a 67 mL solutioncontaining 2 g of dissolved potassium formate at a rate of 23.3 mL/mincausing precipitation of a white product. The product turned light brownduring the course of the reaction. The reaction was held at 40° C. for 5min. The final product was washed to a conductivity of <10 mS and aportion was dried at ambient temperature. The mean grain size wasdetermined by light scattering (HORIBA) to be 48 μm. Optical micrographsof dried product indicated a mean grain size consistent with that foundfrom the light scattering measurement.

Example 6 Inventive, Sodium Propionate (2 g) Added with Silver

A six-liter stainless steel sponge kettle was charged with 2L ofdistilled water and the temperature controlled at 40° C. The reactorcontents were mixed as described in Example 1. To this reactor 71.2 mLof a 3.6M solution of ammonium sulfate was added. Peristaltic pumps wereused to simultaneously deliver a 640 mL solution containing 3.1M silvernitrate at a rate of 225.0 mL/min, a 333 mL solution containing 2.9Mammonium sulfate at a rate of 117.1mL/min and a 67 mL solutioncontaining 2 g of dissolved sodium propionate at a rate of 23.3 mL/mincausing precipitation of a white product. The reaction was held at 40°C. for 5 min. The final product was washed to a conductivity of <10 mSand a portion was dried at ambient temperature. The mean grain size wasdetermined by light scattering (HORIBA) to be 64 μm. Optical micrographsof dried product indicated a mean grain size consistent with that foundfrom the light scattering measurement.

Example 7 Inventive, L-Histidine (2 g) Added with Silver

A six-liter stainless steel sponge kettle was charged with 2L ofdistilled water and the temperature controlled at 40° C. The reactorcontents were mixed as described in Example 1. To this reactor 71.2 mLof a 3.6M solution of ammonium sulfate was added. Peristaltic pumps wereused to simultaneously deliver a 640 mL solution containing 3.1M silvernitrate at a rate of 225.0 mL/min, a 333 mL solution containing 2.9Mammonium sulfate at a rate of 117.1 mL/min and a 67 mL solutioncontaining 2 g of dissolved L-histidine at a rate of 23.3 mL/min causingprecipitation of a white product. The reaction was held at 40° C. for 5min. The final product was washed to a conductivity of <10 mS and aportion was dried at ambient temperature. The mean grain size wasdetermined by light scattering (HORIBA) to be 52 μm. Optical micrographsof dried product indicated a mean grain size consistent with that foundfrom the light scattering measurement.

Table 1 shown below summarizes the particle size results for silversulfate materials precipitated in the presence of monocarboxylic acidadditives or salts thereof.

TABLE 1 Mean Standard Ex. Additive Amount Size Deviation Example No.Additive Addition (g) Mol % (μm) (μm) Type 1 None — — — 76.5 45.2 Comp.2 Ethanol With 2 5.88 88.9 56.2 Comp. silver 3 Ammonium Acetate With 0.50.65 85.5 50.5 Comp. silver 4 Ammonium Acetate With 2 2.595 57.9 28.4Inv. silver 5 Potassium Formate With 2 2.38 48.2 24.9 Inv. silver 6Sodium Propionate With 2 2.08 63.7 29.5 Inv. silver 7 L-Histidine With 21.29 52.3 21.6 Inv. silver

Comparison of the mean grain-size and grain-size distribution (StandardDeviation) results shown above for comparative Examples 2-3 indicatesthat addition of an organic alcohol additive (i.e. ethanol) or a loweramount of ammonium acetate, respectively, increase the particle sizemetrics relative to the no additive comparison of Example 1. Incontrast, Example 4 indicates that addition of a higher amount ofammonium acetate is quite effective in reducing the mean grain-size andgrain-size distribution of silver sulfate relative to the no additivecomparison of Example 1. Similar effects are shown in Examples 5-8,wherein addition of potassium formate, sodium propionate and L-histidineto the precipitation of silver sulfate reduce both the grain-size andthe grain-size distribution relative to the no additive comparison ofExample 1.

Examples 8-15

Examples 8-15 illustrate dicarboxylic acid additives or salts thereof ofthe invention.

Example 8 Inventive, Oxalic Acid (2 g) Added before Silver

A six-liter stainless steel sponge kettle was charged with 2L ofdistilled water and the temperature controlled at 40° C. The reactorcontents were mixed as described in Example 1. To this reactor 71.2 mLof a 3.6M solution of ammonium sulfate and a 67 mL solution containing 2g of dissolved oxalic acid, dihydrate (solution pH adjusted to 5-6 withammonium hydroxide) were added. Peristaltic pumps were used tosimultaneously deliver a 640 mL solution containing 3.1M silver nitrateat a rate of 225.0 mL/min and a 333 mL solution containing 2.9M ammoniumsulfate at a rate of 117.1 mL/min causing precipitation of a whiteproduct. The reaction was held at 40° C. for 5 min. The final productwas washed to a conductivity of <10 mS and a portion was dried atambient temperature. The mean grain size was determined by lightscattering (HORIBA) to be 33 μm.

Example 9 Inventive, Oxalic Acid (2 g) Added with Silver

A six-liter stainless steel sponge kettle was charged with 2L ofdistilled water and the temperature controlled at 40° C. The reactorcontents were mixed as described in Example 1. To this reactor 71.2 mLof a 3.6M solution of ammonium sulfate was added. Peristaltic pumps wereused to simultaneously deliver a 640 mL solution containing 3.1M silvernitrate at a rate of 225.0 mL/min, a 333 mL solution containing 2.9Mammonium sulfate at a rate of 117.1 mL/min and a 67 mL solutioncontaining 2 g of dissolved oxalic acid, dihydrate (solution pH adjustedto 5-6 with ammonium hydroxide) at a rate of 23.3 mL/min causingprecipitation of a white product. The reaction was held at 40° C. for 5min. The final product was washed to a conductivity of <10 mS and aportion was dried at ambient temperature. The mean grain size wasdetermined by light scattering (HORIBA) to be 25 μm. Optical micrographsof dried product indicated a mean grain size consistent with that foundfrom the light scattering measurement.

Example 10 Inventive, Oxalic Acid (2 g) Added after Silver

A six-liter stainless steel sponge kettle was charged with 2L ofdistilled water and the temperature controlled at 40° C. The reactorcontents were mixed as described in Example 1. To this reactor 71.2 mLof a 3.6M solution of ammonium sulfate was added. Peristaltic pumps wereused to simultaneously deliver a 640 mL solution containing 3.1M silvernitrate at a rate of 225.0 mL/min and a 333 mL solution containing 2.9Mammonium sulfate at a rate of 117.1 mL/min causing precipitation of awhite product. After a 5 min hold a peristaltic pump was used to delivera 67 mL solution containing 2 g of dissolved oxalic acid, dihydrate(solution pH adjusted to 5-6 with ammonium hydroxide) at a rate of 23.3mL/min. The reaction was held at 40° C. for 5 min. The final product waswashed to a conductivity of <10 mS and a portion was dried at ambienttemperature. The mean grain size was determined by light scattering(HORIBA) to be 31 μm.

Example 11 Inventive, Malonic Acid (2 g) Added with Silver

A six-liter stainless steel sponge kettle was charged with 2L ofdistilled water and the temperature controlled at 40° C. The reactorcontents were mixed as described in Example 1. To this reactor 71.2 mLof a 3.6M solution of ammonium sulfate was added. Peristaltic pumps wereused to simultaneously deliver a 640 mL solution containing 3.1M silvernitrate at a rate of 225.0 mL/min, a 333 mL solution containing 2.9Mammonium sulfate at a rate of 117.1 mL/min and a 67 mL solutioncontaining 2 g of dissolved malonic acid (solution pH adjusted to 5-6with ammonium hydroxide) at a rate of 23.3 mL/min causing precipitationof a white product. The reaction was held at 40° C. for 5 min. The finalproduct was washed to a conductivity of <10 mS and a portion was driedat ambient temperature. The mean grain size was determined by lightscattering (HORIBA) to be 61 μm. Optical micrographs of dried productindicated a mean grain size consistent with that found from the lightscattering measurement.

Example 12 Inventive, Fumaric Acid (1 g) Added with Silver

A six-liter stainless steel sponge kettle was charged with 2L ofdistilled water and the temperature controlled at 40° C. The reactorcontents were mixed as described in Example 1. To this reactor 71.2 mLof a 3.6M solution of ammonium sulfate was added. Peristaltic pumps wereused to simultaneously deliver a 640 mL solution containing 3.1M silvernitrate at a rate of 225.0 mL/min, a 333 mL solution containing 2.9Mammonium sulfate at a rate of 117.1 mL/min and a 67 mL solutioncontaining 1 g of dissolved fumaric acid (a couple drops of ammoniumhydroxide were used to aid dissolution) at a rate of 23.3 mL/min causingprecipitation of a white product. The reaction was held at 40° C. for 5min. The final product was washed to a conductivity of <10 mS and aportion was dried at ambient temperature. The mean grain size wasdetermined by light scattering (HORIBA) to be 48 μm. Optical micrographsof dried product indicated a mean grain size consistent with that foundfrom the light scattering measurement.

Example 13 Inventive, Malic Acid (2 g) Added with Silver

A six-liter stainless steel sponge kettle was charged with 2L ofdistilled water and the temperature controlled at 40° C. The reactorcontents were mixed as described in Example 1. To this reactor 71.2 mLof a 3.6M solution of ammonium sulfate was added. Peristaltic pumps wereused to simultaneously deliver a 640 mL solution containing 3.1M silvernitrate at a rate of 225.0 mL/min, a 333 mL solution containing 2.9Mammonium sulfate at a rate of 117.1 mL/min and a 67 mL solutioncontaining 2 g of dissolved malic acid (solution pH adjusted to 5-6 withammonium hydroxide) at a rate of 23.3 mL/min causing precipitation of awhite product. The reaction was held at 40° C. for 5 min. The finalproduct was washed to a conductivity of <10 mS and a portion was driedat ambient temperature. The mean grain size was determined by lightscattering (HORIBA) to be 59 μm. Optical micrographs of dried productindicated a mean grain size consistent with that found from the lightscattering measurement.

Example 14 Inventive, Adipic Acid (2 g) Added with Silver

A six-liter stainless steel sponge kettle was charged with 2L ofdistilled water and the temperature controlled at 40° C. The reactorcontents were mixed as described in Example 1. To this reactor 71.2 mLof a 3.6M solution of ammonium sulfate was added. Peristaltic pumps wereused to simultaneously deliver a 640 mL solution containing 3.1M silvernitrate at a rate of 225.0 mL/min, a 333 mL solution containing 2.9Mammonium sulfate at a rate of 117.1 mL/min and a 67 mL solutioncontaining 2 g of dissolved adipic acid (solution pH adjusted to 5-6with ammonium hydroxide) at a rate of 23.3 mL/min causing precipitationof a white product. The reaction was held at 40° C. for 5 min. The finalproduct was washed to a conductivity of <10 mS and a portion was driedat ambient temperature. The mean grain size was determined by lightscattering (HORIBA) to be 33 μm. Optical micrographs of dried productindicated a mean grain size consistent with that found from the lightscattering measurement.

Example 15 Inventive, Isophthalic Acid (2 g) Added with Silver

A six-liter stainless steel sponge kettle was charged with 2 L ofdistilled water and the temperature controlled at 40° C. The reactorcontents were mixed as described in Example 1. To this reactor 71.2 mLof a 3.6M solution of ammonium sulfate was added. Peristaltic pumps wereused to simultaneously deliver a 640 mL solution containing 3.1M silvernitrate at a rate of 225.0 mL/min, a 333 mL solution containing 2.9Mammonium sulfate at a rate of 117.1 mL/min and a 67 mL solutioncontaining 2 g of dissolved isophthalic acid (pH adjusted to ˜5 withammonium hydroxide) at a rate of 23.3 mL/min causing precipitation of awhite product. The reaction was held at 40° C. for 5 min. The finalproduct was washed to a conductivity of <10 mS and a portion was driedat ambient temperature. The mean grain size was determined by lightscattering (HORIBA) to be 52 μm.

Table 2 shown below summarizes the particle size results for silversulfate materials precipitated in the presence of dicarboxylic acidadditives or salts thereof.

TABLE 2 Mean Standard Ex. Additive Amount Size Deviation Example No.Additive Addition (g) Mol % (μm) (μm) Type 1 None — — — 76.5 45.2 Comp.8 Oxalic Acid before 2 1.59 33.4 27.9 Inv. silver 9 Oxalic Acid with 21.59 24.9 12.7 Inv. silver 10 Oxalic Acid after 2 1.59 30.9 30.9 Inv.silver 11 Malonic Acid with 2 1.92 60.8 28.7 Inv. silver 12 Fumaric Acidwith 1 0.86 47.9 28.6 Inv. silver 13 Malic Acid with 2 1.49 59.3 24.3Inv. silver 14 Adipic Acid with 2 1.37 32.6 19.6 Inv. silver 15Isophthalic Acid with 2 1.49 51.5 30.2 Inv. silver

Comparison of the mean grain-size and the grain-size distribution(Standard Deviation) results shown in Table 2 above indicates that foreach inventive example (Examples 8-15) a reduction in both grain-sizeand grain-size distribution (i.e. a more uniform grain-size) of silversulfate is afforded relative to the no additive comparison of Example 1.Comparison of the results for Example 8 and Example 10 to Example 9indicates that oxalic acid is very nearly as effective when added to thereactor either before or after the addition of silver ion.

Example 16

Example 16 illustrates a tetracarboxylic acid additive or salt thereofof the invention.

Example 16 Inventive, EDTA (2 g) Added with Silver

A six-liter stainless steel sponge kettle was charged with 2L ofdistilled water and the temperature controlled at 40° C. The reactorcontents were mixed as described in Example 1. To this reactor 71.2 mLof a 3.6M solution of ammonium sulfate was added. Peristaltic pumps wereused to simultaneously deliver a 640 mL solution containing 3.1M silvernitrate at a rate of 225.0 mL/min, a 333 mL solution containing 2.9Mammonium sulfate at a rate of 117.1 mL/min and a 67 mL solutioncontaining 2 g of dissolved ethylenediaminetetraacetic acid (EDTA),disodium salt dihydrate at a rate of 23.3 mL/min causing precipitationof a white product. The reaction was held at 40° C. for 5 min. The finalproduct was washed to a conductivity of <10 mS and a portion was driedat ambient temperature. The mean grain size was determined by lightscattering (HORIBA) to be 42 μm. Optical micrographs of dried productindicated a mean grain size consistent with that found from the lightscattering measurement.

Table 3 shown below summarizes the particle size results for silversulfate material precipitated in the presence of the sodium salt of atetracarboxylic acid additive.

TABLE 3 Standard Additive Amount Mean Size Deviation Example Ex. No.Additive Addition (g) Mol % (μm) (μm) Type 1 None — — — 76.5 45.2 Comp.16 EDTA with 2 0.54 41.5 25.1 Inv. silver

Comparison of the mean grain-size and the grain-size distribution(Standard Deviation) results shown in Table 3 above indicates thataddition of the sodium salt of EDTA affords a reduction in bothgrain-size and grain-size distribution (i.e. a more uniform grain-size)of silver sulfate relative to the no additive comparison of Example 1.

Examples 17-18

Example 18 illustrates a polymer additive comprising carboxylic acidsubstituents or salts thereof of the invention.

Example 17 Comparative, AQUAZOL-50™ (poly(2-ethyl-2-oxazoline)) (2 g)Added with Silver

A six-liter stainless steel sponge kettle was charged with 2L ofdistilled water and the temperature controlled at 40° C. The reactorcontents were mixed as described in Example 1. To this reactor 71.2 mLof a 3.6M solution of ammonium sulfate was added. Peristaltic pumps wereused to simultaneously deliver a 640 mL solution containing 3.1M silvernitrate at a rate of 225.0 mL/min, a 333 mL solution containing 2.9Mammonium sulfate at a rate of 117.1 mL/min and a 67 mL solutioncontaining 2 g of dissolved AQUAZOL-50™ (poly(2-ethyl-2-oxazoline),50,000 MW) at a rate of 23.3 mL/min causing precipitation of a whiteproduct. The reaction was held at 40° C. for 5 min. The final productwas washed to a conductivity of <10 mS and a portion was dried atambient temperature. The mean grain size was determined by lightscattering (HORIBA) to be 89 μm.

Example 18 Inventive, Polyacrylic acid 5,100 MW (2 g) Added with Silver

A six-liter stainless steel sponge kettle was charged with 2L ofdistilled water and the temperature controlled at 40° C. The reactorcontents were mixed as described in Example 1. To this reactor 71.2 mLof a 3.6M solution of ammonium sulfate was added. Peristaltic pumps wereused to simultaneously deliver a 640 mL solution containing 3.1M silvernitrate at a rate of 225.0 mL/min, a 333 mL solution containing 2.9Mammonium sulfate at a rate of 117.1 mL/min and a 67 mL solutioncontaining 2 g of dissolved polyacrylic acid, sodium salt (5,100 MW,solution pH adjusted to 5-6 with ammonium hydroxide) at a rate of 23.3mL/min causing precipitation of a white product. The reaction was heldat 40° C. for 5 min. The final product was washed to a conductivity of<10 mS and a portion was dried at ambient temperature. The mean grainsize was determined by light scattering (HORIBA) to be 31 μm. Opticalmicrographs of dried product indicated a mean grain size consistent withthat found from the light scattering measurement.

Table 4 shown below summarizes the particle size results for silversulfate materials precipitated in the presence of polymeric additives,one of which comprises carboxylic acid substituents or salts thereof.

TABLE 4 Mean Standard Ex. Additive Amount Size Deviation Example No.Additive Addition (g) Mol % (μm) (μm) Type 1 None — — — 76.5 45.2 Comp.17 Aquazol-50 With silver 2 — 88.9 53.3 Comp. 18 Polyacrylic Acid Withsilver 2 — 31.2 20.8 Inv.

Comparison of the mean grain-size and the grain-size distribution(Standard Deviation) results shown in Table 4 above indicates thatwhereas the addition of AQUAZOL-50™ (poly(2-ethyl-2-oxazoline) polymeradditive increases both particle size metrics, the addition of thesodium salt of polyacrylic acid to the precipitation of silver sulfatereduces both the grain-size and the grain-size distribution (i.e. a moreuniform grain-size) relative to the no additive comparison of Example 1.

Examples 19-22

Examples 19-22 illustrate the incorporation of silver sulfateprecipitated in the presence of the sodium salt of polyacrylic acid incomposites of polypropylene (PP).

Example 19 Comparative, Preparation of PP Check

A Brabender paddle compounder was preheated to 220° C. and the mixingpaddles were set to 60 rpm. Into the feed chamber was charged 40.0 g ofExxon Polypropylene 3155, and compounded 6min under a dry nitrogenpurge. The mixing paddles were stopped, and the feed chamber wasdismantled. The compounded sample was removed from the chamber walls andpaddles, and a composite plaque was produced by pressing the compoundedsample onto a stainless steel plate at a temperature of 22° C. The colorof the solid plaque was clear with a slight whitish haze.

Example 20 Inventive, Silver Sulfate Precipitated with Polyacrylic AcidCompounded in PP

A Brabender paddle compounder was preheated to 220° C. and the mixingpaddles were set to 60 rpm. Into the feed chamber was charged 39.0 g ofExxon Polypropylene 3155, and compounded 2 min under a dry nitrogenpurge. Following the melting of the polyester, 1.0 g of silver sulfatepowder (from Example 18) was added to the feed chamber and the compositewas compounded 4 min under a nitrogen purge. The mixing paddles werestopped, and the feed chamber was dismantled. The compounded sample wasremoved from the chamber walls and paddles, and a composite plaque wasproduced by pressing the compounded sample onto a stainless steel plateat a temperature of 22° C. The color of the solid plaque was lightyellow.

Example 21 Inventive, Silver Sulfate Precipitated with Polyacrylic Acid,Incorporating Iodate, Compounded in PP

A six-liter stainless steel sponge kettle was charged with 2L ofdistilled water and the temperature controlled at 40° C. The reactorcontents were mixed as described in Example 1. To this reactor 71.2 mLof a 3.6M solution of ammonium sulfate was added. Peristaltic pumps wereused to simultaneously deliver a 640 mL solution containing 3.1M silvernitrate at a rate of 225.0 mL/min, a 333 mL solution containing 2.9Mammonium sulfate at a rate of 117.1 mL/min and a 67 mL solutioncontaining 2 g of dissolved polyacrylic acid, sodium salt (5,100 MW,solution pH adjusted to 5-6 with ammonium hydroxide) at a rate of 23.3mL/min causing precipitation of a white product. The reaction was heldat 40° C. for 5 min after which a peristaltic pump delivered a 67 mLsolution containing 1.0 g potassium iodate at a rate of 6.7 mL/min. Thereaction was held at 40° C. for 5 min. The final product was washed to aconductivity of <10 mS and a portion was dried at ambient temperature.

A Brabender paddle compounder was preheated to 220° C. and the mixingpaddles were set to 60 rpm. Into the feed chamber was charged 39.0 g ofExxon Polypropylene 3155, and compounded 2 min under a dry nitrogenpurge. Following the melting of the polyester, 1.0 g of silver sulfatepowder described above was added to the feed chamber and the compositewas compounded 4 min under a nitrogen purge. The mixing paddles werestopped, and the feed chamber was dismantled. The compounded sample wasremoved from the chamber walls and paddles, and a composite plaque wasproduced by pressing the compounded sample onto a stainless steel plateat a temperature of 22° C. The color of the solid plaque was off-white,indicating the presence of iodate reduced discoloration.

Example 22 Inventive, Carver Press Samples Containing PAA in PP forAntimicrobial Evaluation

Composite films (nominally 2-3 mil) were produced from a small portionof the composite plaque generated in Example 20 using a Carver Presspreheated to 182° C. A sandwich was made by placing an aliquot from thecomposite plaque between two polyimide polymer sheets. This sandwich wasplaced on the Carver Press platens, followed by bringing the platenstogether, melting the aliquot from the composite plaque, resulting in afilm between the polyimide sheets. The sandwich was removed from theCarver Press, and the sandwich was quenched at room temperature (22° C.)between two metal plates. The polyimide sheets were peeled away, leavinga freestanding composite film. Several of these composite films weregenerated.

The composite films described above were evaluated for antimicrobialactivity using a modified version of the ASTM E-2149, “Standard TestMethod for Determining the Antimicrobial Activity of ImmobilizedAntimicrobial Agents Under Dynamic Contact Conditions.” In this test,composite films totaling 0.25 g were placed in 125 mL Erlenmeyer flasks.The strips were inoculated with 50 mL containing bacteria (Klebsiellapnuemoniae (ATCC #4352)) or fungi (Aspergillus niger (ATCC #6275)) at10⁵ cells/milliliter. For bacteria, inoculation was carried out alongwith phosphate buffer (pH=7.2) as the medium. The strips were shaken for24 h time periods at ambient temperature on a wrist-action shaker andthen removed from the shaker. Aliquots of 0.1 mL were removed from eachflask and pipetted into test tubes containing 9.9 mL of neutralizingbroth, vortexed, filter plated onto triptocase soy agar at −2 and −4dilutions and then incubated for another 24 h at 35° C. After this finalincubation, the filter plates were examined for bacterial growth and thecolonies counted. For fungi, the strips were subjected to the sameprocedure as the bacteria except they were filter plated onto Sabourauddextrose agar and incubated for 48 h at 28° C. After the 48 h incubationthe filter plates were examined for fungal growth and the coloniescounted.

Antimicrobial test results for Example 22 for Klebsiella pnuemoniae andAspergillus niger reported in terms of percent reduction relative to at=0 sample are contained in Table 5.

TABLE 5 Klebsiella pnuemoniae: Aspergillus niger: 24 h shake/ 24 hshake/ 24 h incubation 48 h incubation Sample (% reduction) (%reduction) Example 22 >99.99 >99.99

Results shown above in Table 5 indicate the silver sulfate precipitatedin the presence of a polymeric additive of the invention is effective inimparting antimicrobial properties when compounded into a film ofpolypropylene.

Examples 23-26

Examples 23-26 illustrate the incorporation of silver sulfateprecipitated in the presence of the sodium salt of polyacrylic acid incomposites of polyethyleneterephthalate (PET).

Example 23 Comparative, Preparation of PET Check

A Brabender paddle compounder was preheated to 270° C. and the mixingpaddles were set to 60 rpm. Into the feed chamber was charged 40.0 g ofEastman Polyester F53HC, and compounded 6min under a dry nitrogen purge.The mixing paddles were stopped, and the feed chamber was dismantled.The compounded sample was removed from the chamber walls and paddles,and a composite plaque was produced by pressing the compounded sampleonto a stainless steel plate at a temperature of 22° C. The color of thesolid plaque was light gray [due to presence of Sb₂O₃ catalyst].

Example 24 Inventive, Silver Sulfate Precipitated with Polyacrylic AcidCompounded in PET

A Brabender paddle compounder was preheated to 270° C. and the mixingpaddles were set to 60 rpm. Into the feed chamber was charged 39.0 g ofEastman Polyester F53HC, and compounded 2 min under a dry nitrogenpurge. Following the melting of the polyester, 1.0 g of silver sulfatepowder (from Example 18) was added to the feed chamber and the compositewas compounded 4 min under a nitrogen purge. The mixing paddles werestopped, and the feed chamber was dismantled. The compounded sample wasremoved from the chamber walls and paddles, and a composite plaque wasproduced by pressing the compounded sample onto a stainless steel plateat a temperature of 22° C. The color of the solid plaque was brown.

Example 25 Inventive, Silver Sulfate Precipitated with Polyacrylic Acid,Incorporating Iodate, Compounded in PET

A Brabender paddle compounder was preheated to 270° C. and the mixingpaddles were set to 60 rpm. Into the feed chamber was charged 39.0 g ofEastman Polyester F53HC, and compounded 2 min under a dry nitrogenpurge. Following the melting of the polyester, 1.0 g of silver sulfatepowder (from Example 18) was added to the feed chamber and the compositewas compounded 4 min under a nitrogen purge. The mixing paddles werestopped, and the feed chamber was dismantled. The compounded sample wasremoved from the chamber walls and paddles, and a composite plaque wasproduced by pressing the compounded sample onto a stainless steel plateat a temperature of 22° C. The color of the solid plaque was lightbrown, indicating the presence of iodate reduced discoloration.

Example 26 Inventive, Carver Press Samples Containing PAA in PET forAntimicrobial Evaluation

Composite films (nominally 2-3 mil) were produced from a small portionof the composite plaque generated in Example 24 using a Carver Presspreheated to 274° C. A sandwich was made by placing an aliquot from thecomposite plaque between two polyimide polymer sheets. This sandwich wasplaced on the Carver Press platens, followed by bringing the platenstogether, melting the aliquot from the composite plaque, resulting in afilm between the polyimide sheets. The sandwich was removed from theCarver Press, and the sandwich was quenched at room temperature (22° C.)between two metal plates. The polyimide sheets were peeled away, leavinga freestanding composite film. Several of these composite films weregenerated.

The composite films described above were evaluated for antimicrobialactivity as described in Example 22. The results are shown in Table 6.

TABLE 6 Klebsiella pnuemoniae: Aspergillus niger: 24 h shake/ 24 hshake/ 24 h incubation 48 h incubation Sample (% reduction) (%reduction) Example 26 >99.99 >99.99

Results shown above in Table 6 indicate the silver sulfate precipitatedin the presence of a polymeric additive of the invention is effective inimparting antimicrobial properties when compounded into a film ofpolyethyleneterephthalate.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

1. A process comprising reacting an aqueous soluble silver salt and anaqueous soluble source of inorganic sulfate ion in an agitatedprecipitation reactor vessel and precipitating particles comprisingprimarily silver sulfate, wherein the reaction and precipitation areperformed in the presence of an aqueous soluble carboxylic acid additiveor salt thereof, the amount of additive being a minor molar percentage,relative to the molar amount of silver sulfate precipitated, andeffective to result in precipitation of particles comprising primarilysilver sulfate having a mean grain-size of less than 70 micrometers. 2.A process according to claim 1, wherein the amount of the carboxylicacid additive or salt thereof present during the precipitation is lessthan 10 molar percent, relative to the molar amount of silver sulfateprecipitated.
 3. A process according to claim 1, wherein the amount ofthe carboxylic acid additive or salt thereof present during theprecipitation is such that the molar percentage of carboxylic acid orcarboxylate groups is greater than 0.7%, relative to the molar amount ofsilver sulfate precipitated.
 4. A process according to claim 1, whereinthe carboxylic acid additive is a monocarboxylic acid or salt thereof.5. A process according to claim 1, wherein the carboxylic acid additiveis a multicarboxylic acid or salt thereof.
 6. A process according toclaim 5, wherein the carboxylic acid additive is a dicarboxylic acid orsalt thereof.
 7. A process according to claim 5, wherein the carboxylicacid additive is a tetracarboxylic acid or salt thereof.
 8. A processaccording to claim 1, wherein an additional additive comprising abromate salt or an iodate salt is present during the precipitation.
 9. Aprocess according to claim 8, wherein the additional additive comprisespotassium iodate.
 10. A process according to claim 1, wherein thecarboxylic acid additive or salt thereof has an aqueous solubility of atleast 1 g/L.
 11. A process according to claim 1, wherein the solublesilver salt comprises silver nitrate, and the soluble source ofinorganic sulfate ion comprises ammonium sulfate.
 12. A processaccording to claim 1, wherein a portion of the solution of the solublesource of inorganic sulfate ion is added simultaneously with thesolution of the soluble silver salt.
 13. A composition of mattercomprising particles of primarily silver sulfate, where the particleshave a mean grain-size of less than 70 micrometers and comprise a minormolar amount, relative to the molar amount of silver sulfate, of acarboxylic acid or salt thereof.
 14. A composition according to claim13, wherein the particles have a mean grain-size of less than 50micrometers.
 15. A composition according to claim 13, wherein theparticles comprise a minor molar amount, relative to the molar amount ofsilver sulfate, of iodate anion.
 16. A composite comprising athermoplastic polymer phase and particles of the composition of claim 13dispersed therein.
 17. A composite according to claim 16, wherein theparticles of primarily silver sulfate have a mean grain-size of lessthan 50 micrometers.
 18. A composite according to claim 16, wherein thepolymer phase is in the form of an extruded film or fiber, or aninjection molded part.
 19. A composite according to claim 16, whereinthe thermoplastic polymer phase comprises a polyolefin.
 20. A compositeaccording to claim 19, wherein the thermoplastic polymer phase comprisespolypropylene.
 21. A composite according to claim 20, where theparticles comprise a minor molar amount, relative to the molar amount ofsilver sulfate, of iodate anion and the polymer phase is in the form ofan extruded film or fiber, or an injection molded part.
 22. A compositeaccording to claim 16, wherein the thermoplastic polymer phase comprisespolyester.
 23. A composite according to claim 22, wherein thethermoplastic polymer phase comprises polyethyleneterephthalate.
 24. Acomposite according to claim 23, where the particles comprise a minormolar amount, relative to the molar amount of silver sulfate, of iodateanion and the polymer phase is in the form of an extruded film or fiber,or an injection molded part.
 25. A composite according to claim 16,where the particles comprise a minor molar amount, relative to the molaramount of silver sulfate, of iodate anion.